draft-ietf-ace-oauth-authz-01.txt   draft-ietf-ace-oauth-authz-02.txt 
ACE Working Group L. Seitz ACE Working Group L. Seitz
Internet-Draft SICS Internet-Draft SICS
Intended status: Standards Track G. Selander Intended status: Standards Track G. Selander
Expires: August 28, 2016 Ericsson Expires: December 12, 2016 Ericsson
E. Wahlstroem E. Wahlstroem
S. Erdtman
Nexus Technology Nexus Technology
S. Erdtman
Spotify AB
H. Tschofenig H. Tschofenig
ARM Ltd. ARM Ltd.
February 25, 2016 June 10, 2016
Authorization for the Internet of Things using OAuth 2.0 Authentication and Authorization for Constrained Environments (ACE)
draft-ietf-ace-oauth-authz-01 draft-ietf-ace-oauth-authz-02
Abstract Abstract
This memo defines how to use OAuth 2.0 as an authorization framework This specification defines the ACE framework for authentication and
with Internet of Things (IoT) deployments, thus bringing a well-known authorization in Internet of Things (IoT) deployments. The ACE
and widely used security solution to IoT devices. Where possible framework is based on a set of building blocks including OAuth 2.0
vanilla OAuth 2.0 is used, but where the limitations of IoT devices and CoAP, thus making a well-known and widely used authorization
require it, profiles and extensions are provided. solution suitable for IoT devices. Existing specifications are used
where possible, but where the limitations of IoT devices require it,
profiles and extensions are provided.
Status of This Memo Status of This Memo
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This Internet-Draft will expire on August 28, 2016. This Internet-Draft will expire on December 12, 2016.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. OAuth 2.0 . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. OAuth 2.0 . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. CoAP . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2. CoAP . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Object Security . . . . . . . . . . . . . . . . . . . . . 8
4. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 9 4. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 9
5. OAuth 2.0 Profiling . . . . . . . . . . . . . . . . . . . . . 12 5. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. Client Information . . . . . . . . . . . . . . . . . . . 12 6. The 'Token' Resource . . . . . . . . . . . . . . . . . . . . 14
5.2. CoAP Access-Token Option . . . . . . . . . . . . . . . . 15 6.1. Client-to-AS Request . . . . . . . . . . . . . . . . . . 14
5.3. Authorization Information Resource at the Resource Server 15 6.2. AS-to-Client Response . . . . . . . . . . . . . . . . . . 17
5.3.1. Authorization Information Request . . . . . . . . . . 16 6.3. Error Response . . . . . . . . . . . . . . . . . . . . . 18
5.3.2. Authorization Information Response . . . . . . . . . 16 6.4. New Request and Response Parameters . . . . . . . . . . . 18
5.3.2.1. Success Response . . . . . . . . . . . . . . . . 16 6.4.1. Grant Type . . . . . . . . . . . . . . . . . . . . . 19
5.3.2.2. Error Response . . . . . . . . . . . . . . . . . 16 6.4.2. Token Type and Algorithms . . . . . . . . . . . . . . 19
5.4. Authorization Information Format . . . . . . . . . . . . 17 6.4.3. Profile . . . . . . . . . . . . . . . . . . . . . . . 20
5.5. CBOR Data Formats . . . . . . . . . . . . . . . . . . . . 17 6.4.4. Confirmation . . . . . . . . . . . . . . . . . . . . 20
5.6. Token Expiration . . . . . . . . . . . . . . . . . . . . 17 6.5. Mapping parameters to CBOR . . . . . . . . . . . . . . . 22
6. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . 18 7. The 'Introspect' Resource . . . . . . . . . . . . . . . . . . 22
6.1. Client and Resource Server are Offline . . . . . . . . . 19 7.1. RS-to-AS Request . . . . . . . . . . . . . . . . . . . . 23
6.2. Resource Server Offline . . . . . . . . . . . . . . . . . 22 7.2. AS-to-RS Response . . . . . . . . . . . . . . . . . . . . 23
6.3. Token Introspection with an Offline Client . . . . . . . 26 7.3. Error Response . . . . . . . . . . . . . . . . . . . . . 24
6.4. Always-On Connectivity . . . . . . . . . . . . . . . . . 30 7.4. Client Token . . . . . . . . . . . . . . . . . . . . . . 25
6.5. Token-less Authorization . . . . . . . . . . . . . . . . 31 7.5. Mapping Introspection parameters to CBOR . . . . . . . . 26
6.6. Securing Group Communication . . . . . . . . . . . . . . 34 8. The Access Token . . . . . . . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 35 8.1. The 'Authorization Information' Resource . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 8.2. Token Expiration . . . . . . . . . . . . . . . . . . . . 28
8.1. CoAP Option Number Registration . . . . . . . . . . . . . 35 9. Security Considerations . . . . . . . . . . . . . . . . . . . 28
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 36 10.1. OAuth Introspection Response Parameter Registration . . 29
10.1. Normative References . . . . . . . . . . . . . . . . . . 36 10.2. OAuth Parameter Registration . . . . . . . . . . . . . . 30
10.2. Informative References . . . . . . . . . . . . . . . . . 38 10.3. OAuth Access Token Types . . . . . . . . . . . . . . . . 30
10.4. Token Type Mappings . . . . . . . . . . . . . . . . . . 30
10.4.1. Registration Template . . . . . . . . . . . . . . . 30
10.4.2. Initial Registry Contents . . . . . . . . . . . . . 31
10.5. JSON Web Token Claims . . . . . . . . . . . . . . . . . 31
10.6. ACE Profile Registry . . . . . . . . . . . . . . . . . . 31
10.6.1. Registration Template . . . . . . . . . . . . . . . 31
10.7. OAuth Parameter Mappings Registry . . . . . . . . . . . 32
10.7.1. Registration Template . . . . . . . . . . . . . . . 32
10.7.2. Initial Registry Contents . . . . . . . . . . . . . 32
10.8. Introspection Resource CBOR Mappings Registry . . . . . 34
10.8.1. Registration Template . . . . . . . . . . . . . . . 35
10.8.2. Initial Registry Contents . . . . . . . . . . . . . 35
10.9. CoAP Option Number Registration . . . . . . . . . . . . 37
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
12.1. Normative References . . . . . . . . . . . . . . . . . . 38
12.2. Informative References . . . . . . . . . . . . . . . . . 38
Appendix A. Design Justification . . . . . . . . . . . . . . . . 40 Appendix A. Design Justification . . . . . . . . . . . . . . . . 40
Appendix B. Roles and Responsibilites -- a Checklist . . . 41 Appendix B. Roles and Responsibilites . . . . . . . . . . . . . 42
Appendix C. Optimizations . . . . . . . . . . . . . . . . . . . 44 Appendix C. Deployment Examples . . . . . . . . . . . . . . . . 44
Appendix D. CoAP and CBOR profiles for OAuth 2.0 . . . . . . . . 45 C.1. Local Token Validation . . . . . . . . . . . . . . . . . 44
D.1. Profile for Token resource . . . . . . . . . . . . . . . 45 C.2. Introspection Aided Token Validation . . . . . . . . . . 48
D.1.1. Token Request . . . . . . . . . . . . . . . . . . . . 46 Appendix D. Document Updates . . . . . . . . . . . . . . . . . . 51
D.1.2. Token Response . . . . . . . . . . . . . . . . . . . 47 D.1. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 52
D.2. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 52
D.2. CoAP Profile for OAuth Introspection . . . . . . . . . . 48 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53
D.2.1. Introspection Request . . . . . . . . . . . . . . . . 48
D.2.2. Introspection Response . . . . . . . . . . . . . . . 49
Appendix E. Document Updates . . . . . . . . . . . . . . . . . . 51
E.1. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
1. Introduction 1. Introduction
Authorization is the process for granting approval to an entity to Authorization is the process for granting approval to an entity to
access a resource [RFC4949]. Managing authorization information for access a resource [RFC4949]. The authorization task itself can best
a large number of devices and users is often a complex task where be described as granting access to a requesting client, for a
dedicated servers are used. resource hosted on a device, the resource server (RS). This exchange
is mediated by one or multiple authorization servers (AS). Managing
authorization for a large number of devices and users is a complex
task.
Managing authorization of users, services and their devices with the We envision that end consumers and enterprises will manage access to
help of dedicated authorization servers (AS) is a common task, found resources on, or produced by, Internet of Things (IoT) devices in the
in enterprise networks as well as on the Web. In its simplest form same style as they do today with data, services and applications on
the authorization task can be described as granting access to a the Web or with their mobile devices. This desire will increase with
requesting client, for a resource hosted on a device, the resource the number of exposed services and capabilities provided by
server (RS). This exchange is mediated by one or multiple applications hosted on the IoT devices.
authorization servers.
We envision that end consumers and enterprises will want to manage While prior work on authorization solutions for the Web and for the
access-control and authorization for their Internet of Things (IoT) mobile environment also applies to the IoT environment many IoT
devices in the same style and this desire will increase with the devices are constrained, for example in terms of processing
number of exposed services and capabilities provided by applications capabilities, available memory, etc. For web applications on
hosted on the IoT devices. The IoT devices may be constrained in constrained nodes this specification makes use of CoAP [RFC7252].
various ways including processing, memory, code-size, energy, etc.,
as defined in [RFC7228], and the different IoT deployments present a
continuous range of device and network capabilities. Taking energy
consumption as an example: At one end there are energy-harvesting or
battery powered devices which have a tight power budget, on the other
end there are devices connected to a continuous power supply which
are not constrained in terms of power, and all levels in between.
Thus IoT devices are very different in terms of available processing
and message exchange capabilities.
This memo describes how to re-use OAuth 2.0 [RFC6749] to extend A detailed treatment of constraints can be found in [RFC7228], and
authorization to Internet of Things devices with different kinds of the different IoT deployments present a continuous range of device
constraints. At the time of writing, OAuth 2.0 is already used with and network capabilities. Taking energy consumption as an example:
certain types of IoT devices and this document will provide
implementers additional guidance for using it in a secure and At one end there are energy-harvesting or battery powered devices
privacy-friendly way. Where possible the basic OAuth 2.0 mechanisms which have a tight power budget, on the other end there are mains-
are used; in some circumstances profiles are defined, for example to powered devices, and all levels in between.
support smaller the over-the-wire message size and smaller code size.
Hence, IoT devices may be very different in terms of available
processing and message exchange capabilities and there is a need to
support many different authorization use cases [RFC7744].
This specification describes a framework for authentication and
authorization in constrained environments (ACE) built on re-use of
OAuth 2.0 [RFC6749], thereby extending authorization to Internet of
Things devices. This specification contains the necessary building
blocks for adjusting OAuth 2.0 to IoT environments.
More detailed, interoperable specifications can be found in profiles.
Implementations may claim conformance with a specific profile,
whereby implementations utilizing the same profile interoperate while
implementations of different profiles are not expected to be
interoperable. Some devices, such as mobile phones and tablets, may
implement multiple profiles and will therefore be able to interact
with a wider range of low end devices.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
Certain security-related terms such as "authentication", Certain security-related terms such as "authentication",
"authorization", "confidentiality", "(data) integrity", "message "authorization", "confidentiality", "(data) integrity", "message
authentication code", and "verify" are taken from [RFC4949]. authentication code", and "verify" are taken from [RFC4949].
Since we describe exchanges as RESTful protocol interactions HTTP Since we describe exchanges as RESTful protocol interactions HTTP
[RFC7231] offers useful terminology. [RFC7231] offers useful terminology.
Terminology for entities in the architecture is defined in OAuth 2.0 Terminology for entities in the architecture is defined in OAuth 2.0
[RFC6749] and [I-D.ietf-ace-actors], such as client (C), resource [RFC6749] and [I-D.ietf-ace-actors], such as client (C), resource
server (RS), and authorization server (AS). OAuth 2.0 uses the term server (RS), and authorization server (AS).
"endpoint" to denote HTTP resources such as /token and /authorize at
the AS, but we will use the term "resource" in this memo to avoid
confusion with the CoAP [RFC7252] term "endpoint".
Since this draft focuses on the problem of access control to Note that the term "endpoint" is used here following its OAuth
definition, which is to denote resources such as /token and
/introspect at the AS and /authz-info at the RS. The CoAP [RFC7252]
definition, which is "An entity participating in the CoAP protocol"
is not used in this memo.
Since this specification focuses on the problem of access control to
resources, we simplify the actors by assuming that the client resources, we simplify the actors by assuming that the client
authorization server (CAS) functionality is not stand-alone but authorization server (CAS) functionality is not stand-alone but
subsumed by either the authorization server or the client (see subsumed by either the authorization server or the client (see
section 2.2 in [I-D.ietf-ace-actors]). section 2.2 in [I-D.ietf-ace-actors]).
3. Overview 3. Overview
This specification describes a framework for authorization in the This specification describes the ACE framework for authorization in
Internet of Things consisting of a set of building blocks. the Internet of Things consisting of a set of building blocks.
The basic block is the OAuth 2.0 [RFC6749] framework, which enjoys The basic block is the OAuth 2.0 [RFC6749] framework, which enjoys
widespread deployment. Many IoT devices can support OAuth 2.0 widespread deployment. Many IoT devices can support OAuth 2.0
without any additional extensions, but for certain constrained without any additional extensions, but for certain constrained
settings additional profiling is needed. settings additional profiling is needed.
Another building block is the lightweight web transfer protocol CoAP Another building block is the lightweight web transfer protocol CoAP
[RFC7252] for those communication environments where HTTP is not [RFC7252] for those communication environments where HTTP is not
appropriate. CoAP typically runs on top of UDP which further reduces appropriate. CoAP typically runs on top of UDP which further reduces
overhead and message exchanges. Transport layer security can be overhead and message exchanges. While this specification defines
provided either by DTLS 1.2 [RFC6347] or TLS 1.2 [RFC5246]. extensions for the use of OAuth over CoAP, we do envision further
underlying protocols to be supported in the future, such as MQTT or
QUIC.
A third building block is CBOR [RFC7049] for encodings where JSON A third building block is CBOR [RFC7049] for encodings where JSON
[RFC7159] is not sufficiently compact. CBOR is a binary encoding [RFC7159] is not sufficiently compact. CBOR is a binary encoding
designed for extremely small code size and fairly small message size. designed for small code and message size, which may be used for
OAuth 2.0 allows access tokens to use different encodings and this encoding of self contained tokens, and also for encoding CoAP POST
document defines such an alternative encoding. The COSE message parameters and CoAP responses.
format [I-D.ietf-cose-msg] is also based on CBOR.
A fourth building block is application layer security, which is used A fourth building block is the compact CBOR-based secure message
where transport layer security is insufficient. At the time of format COSE [I-D.ietf-cose-msg], which enables application layer
writing the preferred approach for securing CoAP at the application security as an alternative or complement to transport layer security
layer is via the use of COSE [I-D.ietf-cose-msg], which adds object (DTLS [RFC6347] or TLS [RFC5246]). COSE is used to secure self
security to CBOR-encoded data. More details about applying COSE to contained tokens such as proof-of-possession (PoP) tokens
CoAP can be found in OSCOAP [I-D.selander-ace-object-security]. [I-D.ietf-oauth-pop-architecture], which is an extension to the OAuth
access tokens, and "client tokens" which are defined in this
framework (see Section 7.4). The default access token format is
defined in CBOR web token (CWT) [I-D.ietf-ace-cbor-web-token].
Application layer security for CoAP using COSE can be provided with
OSCOAP [I-D.selander-ace-object-security].
With the building blocks listed above, solutions satisfying various With the building blocks listed above, solutions satisfying various
IoT device and network constraints are possible. A list of IoT device and network constraints are possible. A list of
constraints is described in detail in RFC 7228 [RFC7228] and a constraints is described in detail in RFC 7228 [RFC7228] and a
description of how the building blocks mentioned above relate to the description of how the building blocks mentioned above relate to the
various constraints can be found in Appendix A. various constraints can be found in Appendix A.
Luckily, not every IoT device suffers from all constraints. The Luckily, not every IoT device suffers from all constraints. The ACE
described framework nevertheless takes all these aspects into account framework nevertheless takes all these aspects into account and
and allows several different deployment variants to co-exist rather allows several different deployment variants to co-exist rather than
than mandating a one-size-fits-all solution. We believe this is mandating a one-size-fits-all solution. We believe this is important
important to cover the wide range of possible interworking use cases to cover the wide range of possible interworking use cases and the
and the different requirements from a security point of view. Once different requirements from a security point of view. Once IoT
IoT deployments mature, popular deployment variants will be deployments mature, popular deployment variants will be documented in
documented in form of profiles. form of ACE profiles.
In the subsections below we provide further details about the In the subsections below we provide further details about the
different building blocks. different building blocks.
3.1. OAuth 2.0 3.1. OAuth 2.0
The OAuth 2.0 authorization framework enables a client to obtain The OAuth 2.0 authorization framework enables a client to obtain
limited access to a resource with the permission of a resource owner. limited access to a resource with the permission of a resource owner.
Authorization related information is passed between the nodes using Authorization information, or references to it, is passed between the
access tokens. These access tokens are issued to clients by an nodes using access tokens. These access tokens are issued to clients
authorization server with the approval of the resource owner. The by an authorization server with the approval of the resource owner.
client uses the access token to access the protected resources hosted The client uses the access token to access the protected resources
by the resource server. hosted by the resource server.
A number of OAuth 2.0 terms are used within this memo: A number of OAuth 2.0 terms are used within this specification:
The token and introspect Endpoints:
The AS hosts the /token endpoint that allows a client to request
access tokens. The client makes a POST request to the /token
endpoint on the AS and receives the access token in the response
(if the request was successful).
The token introspection endpoint, /introspect, is used by the RS
when requesting additional information regarding a received access
token. The RS makes a POST request to /introspect on the AS and
receives information about the access token contain in the
response. (See "Introspection" below.)
Access Tokens: Access Tokens:
Access tokens are credentials used to access protected resources. Access tokens are credentials needed to access protected
An access token is a data structure representing authorization resources. An access token is a data structure representing
permissions issued to the client. Access tokens are generated by authorization permissions issued by the AS to the client. Access
the authorization server and consumed by the resource server. The tokens are generated by the authorization server and consumed by
access token is opaque to the client. the resource server. The access token content is opaque to the
client.
Access tokens can have different formats, and various methods of Access tokens can have different formats, and various methods of
utilization (e.g., cryptographic properties) based on the security utilization (e.g., cryptographic properties) based on the security
requirements of the given deployment. requirements of the given deployment.
Proof of Possession Tokens: Proof of Possession Tokens:
An access token may be bound to a cryptographic key, which is then An access token may be bound to a cryptographic key, which is then
used by an RS to authenticate requests from a client. Such tokens used by an RS to authenticate requests from a client. Such tokens
are called proof-of-possession tokens (or PoP tokens) are called proof-of-possession tokens (or PoP tokens)
[I-D.ietf-oauth-pop-architecture]. [I-D.ietf-oauth-pop-architecture].
The proof-of-possession (PoP) security concept assumes that the AS The proof-of-possession (PoP) security concept assumes that the AS
acts as a trusted third party that binds keys to access tokens. acts as a trusted third party that binds keys to access tokens.
These so called PoP keys are then used by the client to These so called PoP keys are then used by the client to
demonstrate the possession of the secret to the RS when accessing demonstrate the possession of the secret to the RS when accessing
the resource. The RS, when receiving an access token, needs to the resource. The RS, when receiving an access token, needs to
verify that the key used by the client matches the one included in verify that the key used by the client matches the one included in
the access token. When this memo uses the term "access token" it the access token. When this specification uses the term "access
is assumed to be a PoP token unless specifically stated otherwise. token" it is assumed to be a PoP token unless specifically stated
otherwise.
The key bound to the access token (aka PoP key) may be based on The key bound to the access token (aka PoP key) may be based on
symmetric as well as on asymmetric cryptography. The appropriate symmetric as well as on asymmetric cryptography. The appropriate
choice of security depends on the constraints of the IoT devices choice of security depends on the constraints of the IoT devices
as well as on the security requirements of the use case. as well as on the security requirements of the use case.
Symmetric PoP key: Symmetric PoP key: The AS generates a random symmetric PoP key,
encrypts it for the RS and includes it inside an access token.
The AS generates a random symmetric PoP key, encrypts it for The PoP key is also encrypted for the client and sent together
the RS and includes it inside an access token. The PoP key is with the access token to the client.>
also encrypted for the client and sent together with the access
token to the client.
Asymmetric PoP key:
An asymmetric key pair is generated on the client and the Asymmetric PoP key: An asymmetric key pair is generated on the
public key is sent to the AS (if it does not already have client and the public key is sent to the AS (if it does not
knowledge of the client's public key). Information about the already have knowledge of the client's public key).
public key, which is the PoP key in this case, is then included Information about the public key, which is the PoP key in this
inside the access token and sent back to the requesting client. case, is then included inside the access token and sent back to
The RS can identify the client's public key from the the requesting client. The RS can identify the client's public
information in the token, which allows the client to use the key from the information in the token, which allows the client
corresponding private key for the proof of possession. to use the corresponding private key for the proof of
possession.
The access token is protected against modifications using a MAC or The access token is protected against modifications using a MAC or
a digital signature of the AS. The choice of PoP key does not a digital signature, which is added by the AS. The choice of PoP
necessarily imply a specific credential type for the integrity key does not necessarily imply a specific credential type for the
protection of the token. More information about PoP tokens can be integrity protection of the token. More information about PoP
found in [I-D.ietf-oauth-pop-architecture]. tokens can be found in [I-D.ietf-oauth-pop-architecture].
Scopes and Permissions: Scopes and Permissions:
In OAuth 2.0, the client specifies the type of permissions it is In OAuth 2.0, the client specifies the type of permissions it is
seeking to obtain (via the scope parameter) in the access request. seeking to obtain (via the scope parameter) in the access request.
In turn, the AS may use the "scope" response parameter to inform In turn, the AS may use the scope response parameter to inform the
the client of the scope of the access token issued. As the client client of the scope of the access token issued. As the client
could be a constrained device as well, this memo uses CBOR encoded could be a constrained device as well, this specification uses
messages defined in Appendix D to request scopes and to be CBOR encoded messages for CoAP, defined in Section 5, to request
informed what scopes the access token was actually authorized for scopes and to be informed what scopes the access token was
by the AS. actually authorized for by the AS.
The values of the scope parameter are expressed as a list of The values of the scope parameter are expressed as a list of
space- delimited, case-sensitive strings, with a semantic that is space- delimited, case-sensitive strings, with a semantic that is
well-known to the AS and the RS. More details about the concept well-known to the AS and the RS. More details about the concept
of scopes is found under Section 3.3 in [RFC6749]. of scopes is found under Section 3.3 in [RFC6749].
Claims: Claims:
The information carried in the access token in the form of type- Information carried in the access token, called claims, is in the
value pairs is called claims. An access token may for example form of type-value pairs. An access token may, for example,
include a claim about the AS that issued the token (the "iss" include a claim identifying the AS that issued the token (via the
claim) and what audience the access token is intended for (the "iss" claim) and what audience the access token is intended for
"aud" claim). The audience of an access token can be a specific (via the "aud" claim). The audience of an access token can be a
resource or one or many resource servers. The resource owner specific resource or one or many resource servers. The resource
policies influence the what claims are put into the access token owner policies influence what claims are put into the access token
by the authorization server. by the authorization server.
While the structure and encoding of the access token varies While the structure and encoding of the access token varies
throughout deployments, a standardized format has been defined throughout deployments, a standardized format has been defined
with the JSON Web Token (JWT) [RFC7519] where claims are encoded with the JSON Web Token (JWT) [RFC7519] where claims are encoded
as a JSON object. In [I-D.wahlstroem-ace-cbor-web-token] an as a JSON object. In [I-D.ietf-ace-cbor-web-token] an equivalent
equivalent format using CBOR encoding (CWT) has been defined. format using CBOR encoding (CWT) has been defined.
Introspection: Introspection:
Introspection is a method for a resource server to query the Introspection is a method for a resource server to query the
authorization server for the active state and content of a authorization server for the active state and content of a
received access token. This is particularly useful in those cases received access token. This is particularly useful in those cases
where the authorization decisions are very dynamic and/or where where the authorization decisions are very dynamic and/or where
the received access token itself is a reference rather than a the received access token itself is a reference rather than a
self-contained token. More information about introspection in self-contained token. More information about introspection in
OAuth 2.0 can be found in [I-D.ietf-oauth-introspection]. OAuth 2.0 can be found in [RFC7662].
3.2. CoAP 3.2. CoAP
CoAP is an application layer protocol similar to HTTP, but CoAP is an application layer protocol similar to HTTP, but
specifically designed for constrained environments. CoAP typically specifically designed for constrained environments. CoAP typically
uses datagram-oriented transport, such as UDP, where reordering and uses datagram-oriented transport, such as UDP, where reordering and
loss of packets can occur. A security solution need to take the loss of packets can occur. A security solution need to take the
latter aspects into account. latter aspects into account.
While HTTP uses headers and query-strings to convey additional While HTTP uses headers and query-strings to convey additional
information about a request, CoAP encodes such information in so- information about a request, CoAP encodes such information in so-
called 'options'. called 'options'.
CoAP supports application-layer fragmentation of the CoAP payloads CoAP supports application-layer fragmentation of the CoAP payloads
through blockwise transfers [I-D.ietf-core-block]. However, this through blockwise transfers [I-D.ietf-core-block]. However, block-
method does not allow the fragmentation of large CoAP options, wise transfer does not increase the size limits of CoAP options,
therefore data encoded in options has to be kept small. therefore data encoded in options has to be kept small.
3.3. Object Security Transport layer security for CoAP can be provided by DTLS 1.2
[RFC6347] or TLS 1.2 [RFC5246]. CoAP defines a number of proxy
Transport layer security is not always sufficient and application operations which requires transport layer security to be terminated
layer security has to be provided. COSE [I-D.ietf-cose-msg] defines at the proxy. One approach for protecting CoAP communication end-to-
a message format for cryptographic protection of data using CBOR end through proxies, and also to support security for CoAP over
encoding. There are two main approaches for application layer different transport in a uniform way, is to provide security on
security: application layer using an object-based security mechanism such as
CBOR Encoded Message Syntax [I-D.ietf-cose-msg].
Object Security of CoAP (OSCOAP)
OSCOAP [I-D.selander-ace-object-security] is a method for
protecting CoAP request/response message exchanges, including CoAP
payloads, CoAP header fields as well as CoAP options. OSCOAP
provides end-to-end confidentiality, integrity and replay
protection, and a secure binding between CoAP request and response
messages.
A CoAP message protected with OSCOAP contains the CoAP option
"Object-Security" which signals that the CoAP message carries a
COSE message ([I-D.ietf-cose-msg]). OSCOAP defines a profile of
COSE which includes replay protection.
Object Security of Content (OSCON)
For the case of wrapping of application layer payload data
("content") only, such as resource representations or claims of
access tokens, the same COSE profile can be applied to obtain end-
to-end confidentiality, integrity and replay protection.
[I-D.selander-ace-object-security] defines this functionality as
Object Security of Content (OSCON).
In this case, the message is not bound to the underlying One application of COSE is OSCOAP [I-D.selander-ace-object-security],
application layer protocol and can therefore be used with HTTP, which provides end-to-end confidentiality, integrity and replay
CoAP, Bluetooth Smart, etc. While OSCOAP integrity protects protection, and a secure binding between CoAP request and response
specific CoAP message meta-data like request/response code, and messages. In OSCOAP, the CoAP messages are wrapped in COSE objects
binds a response to a specific request, OSCON protects only and sent using CoAP.
payload/content, therefore those security features are lost. The
advantages are that an OSCON message can be passed across
different protocols, from request to response, and used to secure
group communications.
4. Protocol Interactions 4. Protocol Interactions
This framework is based on the same protocol interactions as OAuth The ACE framework is based on the OAuth 2.0 protocol interactions
2.0: A client obtains an access token from an AS and presents the using the /token and /introspect endpoints. A client obtains an
token to an RS to gain access to a protected resource. These access token from an AS using the /token endpoint and subsequently
interactions are shown in Figure 1. An overview of various OAuth presents the access token to a RS to gain access to a protected
concepts is provided in Section 3.1. resource. The RS, after receiving an access token, may present it to
the AS via the /introspect endpoint to get information about the
access token. In other deployments the RS may process the access
token locally without the need to contact an AS. These interactions
are shown in Figure 1. An overview of various OAuth concepts is
provided in Section 3.1.
The consent of the resource owner, for giving a client access to a The consent of the resource owner, for giving a client access to a
protected resource, can be pre-configured authorization policies or protected resource, can be pre-configured authorization policies or
dynamically at the time when the request is sent. The resource owner dynamically at the time when the request is sent. The resource owner
and the requesting party (= client owner) are not shown in Figure 1. and the requesting party (i.e. client owner) are not shown in
Figure 1.
For the description in this document we assume that the client has This framework supports a wide variety of communication security
been registered to an AS. Registration means that the two share mechanisms between the ACE entities, such as client, AS, and RS. We
credentials, configuration parameters and that some form of assume that the client has been registered (also called enrolled or
authorization has taken place. These credentials are used to protect onboarded) to an AS using a mechanism defined outside the scope of
the token request by the client and the transport of access tokens this document. In practice, various techniques for onboarding have
and client information from AS to the client. been used, such as factory-based provisioning or the use of
commissioning tools. Regardless of the onboarding technique, this
registration procedure implies that the client and the AS share
credentials, and configuration parameters. These credentials are
used to mutually authenticate each other and to protect messages
exchanged between the client and the AS.
It is also assumed that the RS has been registered with the AS. It is also assumed that the RS has been registered with the AS,
Established keying material between the AS and the RS allows the AS potentially in a similar way as the client has been registered with
to apply cryptographic protection to the access token to ensure that the AS. Established keying material between the AS and the RS allows
the content cannot be modified, and if needed, that the content is the AS to apply cryptographic protection to the access token to
confidentiality protected. ensure that its content cannot be modified, and if needed, that the
content is confidentiality protected.
The keying material necessary for establishing communication security The keying material necessary for establishing communication security
between C and RS is dynamically established as part of the protocol between C and RS is dynamically established as part of the protocol
described in this document. described in this document.
At the start of the protocol there is an optional discovery step At the start of the protocol there is an optional discovery step
where the client discovers the resource server and the resources this where the client discovers the resource server and the resources this
server hosts. In this step the client might also determine what server hosts. In this step the client might also determine what
permissions are needed to access the protected resource. The exact permissions are needed to access the protected resource. The
procedure depends on the protocols being used and the specific detailed procedures for this discovery process may be defined in an
deployment environment. In Bluetooth Smart, for example, ACE profile and depend on the protocols being used and the specific
advertisements are broadcasted by a peripheral, including information deployment environment.
about the supported services. In CoAP, as a second example, a client
can makes a request to "/.well-known/core" to obtain information
about available resources, which are returned in a standardized
format as described in [RFC6690].
+--------+ +---------------+ In Bluetooth Low Energy, for example, advertisements are broadcasted
| |---(A)-- Token Request ------------->| | by a peripheral, including information about the primary services.
| | | Authorization | In CoAP, as a second example, a client can makes a request to
| |<--(B)-- Access Token ---------------| Server | "/.well-known/core" to obtain information about available resources,
| | + Client Information | | which are returned in a standardized format as described in
| | +---------------+ [RFC6690].
| | ^ |
| | Introspection Request & Response (D)| |(E)
| Client | | v
| | +--------------+
| |---(C)-- Token + Request ----------->| |
| | | Resource |
| |<--(F)-- Protected Resource ---------| Server |
| | | |
+--------+ +--------------+
Figure 1: Overview of the basic protocol flow +--------+ +---------------+
| |---(A)-- Token Request ------->| |
| | | Authorization |
| |<--(B)-- Access Token ---------| Server |
| | + Client Information | |
| | +---------------+
| | ^ |
| | Introspection Request (D)| |
| Client | | |
| | Response + Client Token | |(E)
| | | v
| | +--------------+
| |---(C)-- Token + Request ----->| |
| | | Resource |
| |<--(F)-- Protected Resource ---| Server |
| | | |
+--------+ +--------------+
Figure 1: Basic Protocol Flow.
Requesting an Access Token (A): Requesting an Access Token (A):
The client makes an access token request to the AS. This memo The client makes an access token request to the /token endpoint at
assumes the use of PoP tokens (see Section 3.1 for a short the AS. This framework assumes the use of PoP tokens (see
description) wherein the AS binds a key to an access token. The Section 3.1 for a short description) wherein the AS binds a key to
client may include permissions it seeks to obtain, and information an access token. The client may include permissions it seeks to
about the type of credentials it wants to use (i.e., symmetric or obtain, and information about the credentials it wants to use
asymmetric cryptography). (e.g., symmetric/asymmetric cryptography or a reference to a
specific credential).
Access Token Response (B): Access Token Response (B):
If the AS successfully processes the request from the client, it If the AS successfully processes the request from the client, it
returns an access token. It also includes various parameters, returns an access token. It also returns various parameters,
which we call "Client Information". In addition to the response referred as "Client Information". In addition to the response
parameters defined by OAuth 2.0 and the PoP token extension, we parameters defined by OAuth 2.0 and the PoP token extension,
consider new kinds of response parameters in Section 5, including further response parameters, such as information on which profile
information on which security protocol the client should use with the client should use with the resource server(s). More
the resource server(s) that it has just been authorized to access. information about these parameters can be found in in Section 6.4.
Communication security between client and RS may be based on pre-
provisioned keys/security contexts or dynamically established.
The RS authenticates the client via the PoP token; and the client
authenticates the RS via the client information as described in
Section 5.1.
Resource Request (C): Resource Request (C):
The client interacts with the RS to request access to the The client interacts with the RS to request access to the
protected resource and provides the access token. The protocol to protected resource and provides the access token. The protocol to
use between the client and the RS is not restricted to CoAP; HTTP, use between the client and the RS is not restricted to CoAP.
HTTP/2, Bluetooth Smart etc., are also possible candidates. HTTP, HTTP/2, QUIC, MQTT, Bluetooth Low Energy, etc., are also
viable candidates.
Depending on the device limitations and the selected protocol this Depending on the device limitations and the selected protocol this
exchange may be split up into two phases: exchange may be split up into two parts:
(1) the client sends the access token to a newly defined
authorization endpoint at the RS (see Section 5.3) , which
conveys authorization information to the RS that may be used by
the client for subsequent resource requests, and
(1) the client sends the access token containing, or
referencing, the authorization information to the RS, that may
be used for subsequent resource requests by the client, and
(2) the client makes the resource access request, using the (2) the client makes the resource access request, using the
communication security protocol and other client information communication security protocol and other client information
obtained from the AS. obtained from the AS.
The RS verifies that the token is integrity protected by the AS The Client and the RS mutually authenticate using the security
and compares the claims contained in the access token with the protocol specified in the profile (see step B) and the keys
resource request. If the RS is online, validation can be handed obtained in the access token or the client information or the
over to the AS using token introspection (see messages D and E) client token. The RS verifies that the token is integrity
over HTTP or CoAP, in which case the different parts of step C may protected by the AS and compares the claims contained in the
be interleaved with introspection. access token with the resource request. If the RS is online,
validation can be handed over to the AS using token introspection
(see messages D and E) over HTTP or CoAP, in which case the
different parts of step C may be interleaved with introspection.
Token Introspection Request (D): Token Introspection Request (D):
A resource server may be configured to use token introspection to A resource server may be configured to introspect the access token
interact with the AS to obtain the most recent claims, such as by including it in a request to the /introspect endpoint at that
scope, audience, validity etc. associated with a specific access AS. Token introspection over CoAP is defined in Section 7 and for
token. Token introspection over CoAP is defined in HTTP in [RFC7662].
[I-D.wahlstroem-ace-oauth-introspection] and for HTTP in
[I-D.ietf-oauth-introspection].
Note that token introspection is an optional step and can be Note that token introspection is an optional step and can be
omitted if the token is self-contained and the resource server is omitted if the token is self-contained and the resource server is
prepared to perform the token validation on its own. prepared to perform the token validation on its own.
Token Introspection Response (E): Token Introspection Response (E):
The AS validates the token and returns the claims associated with The AS validates the token and returns the most recent parameters,
it back to the RS. The RS then uses the received claims to such as scope, audience, validity etc. associated with it back to
process the request to either accept or to deny it. the RS. The RS then uses the received parameters to process the
request to either accept or to deny it. The AS can additionally
return information that the RS needs to pass on to the client in
the form of a client token. The latter is used to establish keys
for mutual authentication between client and RS, when the client
has no direct connectivity to the AS.
Protected Resource (F): Protected Resource (F):
If the request from the client is authorized, the RS fulfills the If the request from the client is authorized, the RS fulfills the
request and returns a response with the appropriate response code. request and returns a response with the appropriate response code.
The RS uses the dynamically established keys to protect the The RS uses the dynamically established keys to protect the
response, according to used communication security protocol. response, according to used communication security protocol.
5. OAuth 2.0 Profiling 5. Framework
This section describes profiles of OAuth 2.0 adjusting it to The following sections detail the profiling and extensions of OAuth
constrained environments for use cases where this is necessary. 2.0 for constrained environments which constitutes the ACE framework.
Profiling for JSON Web Tokens (JWT) is provided in
[I-D.wahlstroem-ace-cbor-web-token].
5.1. Client Information Credential Provisioning
OAuth 2.0 using bearer tokens, as described in [RFC6749] and in For IoT we cannot generally assume that the client and RS are part
[RFC6750], requires TLS for all communication interactions between of a common key infrastructure, so the AS provisions credentials
client, authorization server, and resource server. This is possible or associated information to allow mutual authentication. These
in the scope where OAuth 2.0 was originally developed: web and mobile credentials need to be provided to the parties before or during
applications. In these environments resources like computational the authentication protocol is executed, and may be re-used for
power and bandwidth are not scarce and operating systems as well as subsequent token requests.
browser platforms are pre-provisioned with trust anchors that enable
clients to authenticate servers based on the Web PKI. In a more
heterogeneous IoT environment a wider range of use cases needs to be
supported. Therefore, this document suggests extensions to OAuth 2.0
that enables the AS to inform the client on how to communicate
securely with a RS and that allows the client to indicate
communication security preferences to the AS.
In the OAuth memo defining the key distribution for proof-of- Proof-of-Possession
possession (PoP) tokens [I-D.ietf-oauth-pop-key-distribution], the
authors suggest to use Uri-query parameters in order to submit the
parameters of the client's token request. To avoid large headers if
the client uses CoAP to communicate with the AS, this memo specifies
the following alternative for submitting client request parameters to
the AS: The client encodes the parameters of it's request as a CBOR
map and submits that map as the payload of the client request. The
Content-format MUST be application/cbor in that case.
The OAuth memo further specifies that the AS SHALL use a JSON The ACE framework by default implements proof-of-possession for
structure in the payload of the response to encode the response access tokens, i.e. that the authenticated token holder is bound
parameters. These parameters include the access token, destined for to the token. The binding is provided by the "cnf" claim
the RS and additional information for the client, such as e.g. the indicating what key is used for mutual authentication. If clients
PoP key. We call this information "client information". If the need to update a token, e.g. to get additional rights, they can
client is using CoAP to communicate with the AS the AS SHOULD use request that the AS binds the new access token to the same
CBOR instead of JSON for encoding it's response. The client can credential as the previous token.
explicitly request this encoding by using the CoAP Accept option.
If the channel between client and AS is not secure, the whole ACE Profile Negotiation
messages from client to AS and vice-versa MUST be wrapped in JWEs
[RFC7516] or COSE_Encrypted structures [I-D.ietf-cose-msg].
The client may be a constrained device and could therefore be limited The client or RS may be limited in the encodings or protocols it
in the communication security protocols it supports. It can supports. To support a variety of different deployment settings,
therefore signal to the AS which protocols it can support for specific interactions between client and RS are defined in an ACE
securing their mutual communication. This is done by using the "csp" profile. The ACE framework supports the negotiation of different
parameter defined below in the Token Request message sent to the AS. ACE profiles between client and AS using the "profile" parameter
in the token request and token response.
Note that The OAuth key distribution specification OAuth 2.0 requires the use of TLS both to protect the communication
[I-D.ietf-oauth-pop-key-distribution] describes in section 6 how the between AS and client when requesting an access token and between AS
client can request specific types of keys (symmetric vs. asymmetric) and RS for introspection. In constrained settings TLS is not always
and proof-of-possession algorithms in the PoP token request. feasible, or desirable. Nevertheless it is REQUIRED that the data
exchanged with the AS is encrypted and integrity protected. It is
furthermore REQUIRED that the AS and the endpoint communicating with
it (client or RS) perform mutual authentication.
The client and the RS might not have any prior knowledge about each Profiles are expected to specify the details of how this is done,
other, therefore the AS needs to help them to establish a security depending e.g. on the communication protocol and the credentials used
context or at least a key. The AS does this by indicating by the client or the RS.
communication security protocol ("csp") and additional key parameters
in the client information.
The "csp" parameter specifies how client and RS communication is In OAuth 2.0 the communication with the Token and the Introspection
going to be secured based on returned keys. Currently defined values resources at the AS is assumed to be via HTTP and may use Uri-query
are "TLS", "DTLS", "ObjectSecurity" with the encodings specified in parameters. This framework RECOMMENDS to use CoAP instead and
Figure 2. Depending on the value different additional parameters RECOMMENDS the use of the following alternative instead of Uri-query
become mandatory. parameters: The sender (client or RS) encodes the parameters of its
request as a CBOR map and submits that map as the payload of the POST
request. The Content-format MUST be "application/cbor" in that case.
/-----------+--------------+-----------------------\ The OAuth 2.0 AS uses a JSON structure in the payload of its
| Value | Major Type | Key | responses both to client and RS. This framework RECOMMENDS the use
|-----------+--------------+-----------------------| of CBOR [RFC7049] instead. The requesting device can explicitly
| 0 | 0 | TLS | request this encoding by setting the CoAP Accept option in the
| 1 | 0 | DTLS | request to "application/cbor".
| 2 | 0 | ObjectSecurity |
\-----------+--------------+-----------------------/
Figure 2: Table of 'csp' parameter value encodings for Client 6. The 'Token' Resource
Information.
CoAP specifies three security modes of DTLS: PreSharedKey, In plain OAuth 2.0 the AS provides the /token resource for submitting
RawPublicKey and Certificate. The same modes may be used with TLS. access token requests. This framework extends the functionality of
The client is to infer from the type of key provided, which (D)TLS the /token resource, giving the AS the possibility to help client and
mode the RS supports as follows. RS to establish shared keys or to exchange their public keys.
If PreSharedKey mode is used, the AS MUST provide the client with the Communication between the client and the token resource at the AS
pre-shared key to be used with the RS. This key MUST be the same as MUST be integrity protected and encrypted. Furthermore AS and client
the PoP key (i.e. a symmetric key as in section 4 of MUST perform mutual authentication. Profiles of this framework are
[I-D.ietf-oauth-pop-key-distribution]). expected to specify how authentication and communication security is
implemented.
The client MUST use the PoP key as DTLS pre-shared key. The client The figures of this section uses CBOR diagnostic notation without the
MUST furthermore use the "kid" parameter provided as part of the JWK/ integer abbreviations for the parameters or their values for better
COSE_Key as the psk_identity in the DTLS handshake [RFC4279]. readability.
If RawPublicKey mode is used, the AS MUST provide the client with the 6.1. Client-to-AS Request
RS's raw public key using the "rpk" parameter defined in the
following. This parameter MUST contain a JWK or a COSE_Key. The
client MUST provide a raw public key to the AS, and the AS MUST use
this key as PoP key in the token. The token MUST thus use asymmetric
keys for the proof-of-possession.
In order to get the proof-of-possession a RS configured to use this When requesting an access token from the AS, the client MAY include
mode together with PoP tokens MUST require client authentication in the following parameters in the request in addition to the ones
the DTLS handshake. The client MUST use the raw public key bound to required or optional according to the OAuth 2.0 specification
the PoP token for client authentication in DTLS. [RFC6749]:
TLS or DTLS with certificates MAY make use of pre-established trust token_type
anchors or MAY be configured more tightly with additional client OPTIONAL. See Section 6.4 for more details.
information parameters, such as x5c, x5t, or x5t#S256. An overview
of these parameters is given below.
For when communication security is based on certificates this alg
attribute can be used to define the server certificate or CA OPTIONAL. See Section 6.4 for more details.
certificate. Semantics for this attribute is defined by [RFC7517] or
COSE_Key [I-D.ietf-cose-msg].
For when communication security is based on certificates this profile
attribute can be used to define the specific server certificate to OPTIONAL. This indicates the profile that the client would like
expect or the CA certificate. Semantics for this attribute is to use with the RS. See Section 6.4 for more details on the
defined by JWK/COSE_Key. formatting of this parameter. If the RS cannot support the
requested profile, the AS MUST reply with an error message.
To use object security (such as OSCOAP and OSCON) requires security cnf
context to be established, which can be provisioned with PoP token OPTIONAL. This field contains information about a public key the
and client information, or derived from that information. Object client would like to bind to the access token. If the client
security specifications designed to be used with this protocol MUST requests an asymmetric proof-of-possession algorithm, but does not
specify the parameters that an AS has to provide to the client in provide a public key, the AS MUST respond with an error message.
order to set up the necessary security context. See Section 6.4 for more details on the formatting of the 'cnf'
parameter.
The RS may support different ways of receiving the access token from These new parameters are optional in the case where the AS has prior
the client (see Section 5.3 and Appendix C). The AS MAY signal the knowledge of the capabilities of the client, otherwise these
required method for access token transfer in the client information parameters are required. This prior knowledge may, for example, be
by using the "tktr" (token transport) parameter using the values set by the use of a dynamic client registration protocol exchange
defined in table Figure 3. If no "tktn" parameter is present, the [RFC7591].
client MUST use the default Authorization Information resource as
specified in Section 5.3.
/-----------+--------------+-------------------------\ The following examples illustrate different types of requests for
| Value | Major Type | Key | proof-of-possession tokens.
|-----------+--------------+-------------------------|
| 0 | 0 | POST to /authz-info |
| 1 | 0 | RFC 4680 |
| 2 | 0 | CoAP option "Ref-Token" |
\-----------+--------------+-------------------------/
Figure 3: Table of 'tktn' parameter value encodings for Client Figure 2 shows a request for a token with a symmetric proof-of-
Information. possession key.
Table Figure 4 summarizes the additional parameters defined here for Header: POST (Code=0.02)
use by the client or the AS in the PoP token request protocol. Uri-Host: "server.example.com"
Uri-Path: "token"
Content-Type: "application/cbor"
Payload:
{
"grant_type" : "client_credentials",
"aud" : "tempSensor4711",
"client_id" : "myclient",
"client_secret" : b64'FWRUVGZUZmZFRkWSRlVGhA',
"token_type" : "pop",
"alg" : "HS256",
"profile" : "coap_dtls"
}
/-----------+--------------+----------------------------------\ Figure 2: Example request for an access token bound to a symmetric
| Parameter | Used by | Description | key.
|-----------+--------------+----------------------------------|
| csp | client or AS | Communication security protocol |
| rpk | AS | RS's raw public key |
| x5c | AS | RS's X.509 certificate chain |
| x5t | AS | RS's SHA-1 cert thumb print |
| x5t#S256 | AS | RS's SHA-256 cert thumb print |
| tktn | AS | Mode of token transfer C -> RS |
\-----------+--------------+----------------------------------/
Figure 4: Table of additional parameters defined for the PoP Figure 3 shows a request for a token with an asymmetric proof-of-
protocol. possession key.
5.2. CoAP Access-Token Option Header: POST (Code=0.02)
Uri-Host: "server.example.com"
Uri-Path: "token"
Content-Type: "application/cbor"
Payload:
{
"grant_type" : "token",
"aud" : "lockOfDoor0815",
"client_id" : "myclient",
"token_type" : "pop",
"alg" : "ES256",
"profile" : "coap_oscoap"
"cnf" : {
"COSE_Key" : {
"kty" : "EC",
"kid" : h'11',
"crv" : "P-256",
"x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
"y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
}
}
}
OAuth 2.0 access tokens are usually transferred as authorization Figure 3: Example request for an access token bound to an asymmetric
header. CoAP has no authorization header equivalence. This document key.
therefor register the option Access-Token. The Access-Token option
is an alternative for transferring the access token when it is
smaller then 255 bytes. If token is larger the 255 bytes lager
authorization information resources MUST at the RS be user when CoAP.
5.3. Authorization Information Resource at the Resource Server Figure 4 shows a request for a token where a previously communicated
proof-of-possession key is only referenced.
A consequence of allowing the use of CoAP as web transfer protocol is Header: POST (Code=0.02)
that we cannot rely on HTTP specific mechanisms, such as transferring Uri-Host: "server.example.com"
information elements in HTTP headers since those are not necessarily Uri-Path: "token"
gracefully mapped to CoAP. In case the access token is larger than Content-Type: "application/cbor"
255 bytes it should not be sent as a CoAP option. Payload:
{
"grant_type" : "client_credentials",
"aud" : "valve424",
"scope" : "read",
"client_id" : "myclient",
"token_type" : "pop",
"alg" : "ES256",
"profile" : "coap_oscoap"
"cnf" : {
"kid" : b64'6kg0dXJM13U'
}
}
For conveying authorization information to the RS a new resource is Figure 4: Example request for an access token bound to a key
introduced to which the PoP tokens can be sent to convey reference.
authorization information before the first resource request is made
by the client. This specification calls this resource "/authz-info";
the URI may, however, vary in deployments.
The RS needs to store the PoP token for when later authorizing 6.2. AS-to-Client Response
requests from the client. The RS is not mandated to be able to
manage multiple client at once. how the RS manages clients is out of
scope for this specification.
5.3.1. Authorization Information Request If the access token request has been successfully verified by the AS
and the client is authorized to obtain a PoP token for the indicated
audience and scopes (if any), the AS issues an access token. If
client authentication failed or is invalid, the authorization server
returns an error response as described in Section 6.3.
The client makes a POST request to the authorization information The following parameters may also be part of a successful response in
resource by sending its PoP token as request data. addition to those defined in section 5.1 of [RFC6749]:
Client MUST send the Content-Format option indicate token format profile
REQUIRED. This indicates the profile that the client MUST use
towards the RS. See Section 6.4 for the formatting of this
parameter.
5.3.2. Authorization Information Response cnf
REQUIRED. This field contains information about the proof-of
possession key for this access token. See Section 6.4 for the
formatting of this parameter.
The RS MUST resonde to a requests to the authorization information Note that the access token can also contains a 'cnf' claim, however,
resource. The response MUST match CoAP response codes according to these two values are consumed by different parties. The access token
success or error response section is created by the AS and processed by the RS (and opaque to the
client) whereas the Client Information is created by the AS and
processed by the client; it is never forwarded to the resource
server.
5.3.2.1. Success Response The following examples illustrate different types of responses for
proof-of-possession tokens.
Successful requests MUST be answered with 2.01 Created to indicate Figure 5 shows a response containing a token and a 'cnf' parameter
that a "session" for the PoP Token has been created. No location with a symmetric proof-of-possession key.
path is required to be returned.
Resource Header: Created (Code=2.01)
Client Server Content-Type: "application/cbor"
| | Payload:
| | {
A: +-------->| Header: POST (Code=0.02) "access_token" : b64'SlAV32hkKG ...
| POST | Uri-Path: "/authz-info" (remainder of CWT omitted for brevity;
| | Content-Format: "application/cwt" CWT contains COSE_Key in the 'cnf' claim)',
| | Payload: <PoP Token> "token_type" : "pop",
| | "alg" : "HS256",
B: |<--------+ Header: 2.01 Created "expires_in" : "3600",
| 2.01 | "profile" : "coap_dtls"
| | "cnf" : {
"COSE_Key" : {
"kty" : "Symmetric",
"kid" : b64'39Gqlw',
"k" : b64'hJtXhkV8FJG+Onbc6mxCcQh'
}
}
}
Figure 5: Authorization Information Resource Success Response Figure 5: Example AS response with an access token bound to a
symmetric key.
5.3.2.2. Error Response 6.3. Error Response
The resource server MUST user appropriate CoAP response code to The error responses for CoAP-based interactions with the AS are
convey the error to the Client. For request that are not valid, e.g. equivalent to the ones for HTTP-based interactions as defined in
unknown Content-Format, 4.00 Bad Request MUST be returned. If token section 5.2 of [RFC6749], with the following differences: The
is not valid, e.g. wrong audience, the RS MUST return 4.01 Content-Type MUST be set to "application/cbor", the payload MUST be
Unauthorized. encoded in a CBOR map and the CoAP response code 4.00 Bad Request
MUST be used unless specified otherwise.
Resource 6.4. New Request and Response Parameters
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/authz-info"
| | Content-Format: "application/cwt"
| | Payload: <PoP Token>
| |
B: |<--------+ Header: 4.01 Unauthorized
| 2.01 |
| |
Figure 6: Authorization Information Resource Error Response This section defines parameters that can be used in access token
requests and responses, as well as abbreviations for more compact
encoding of existing parameters and common values.
5.4. Authorization Information Format 6.4.1. Grant Type
We introduce a new claim for describing access rights with a specific The abbreviations in Figure 6 MAY be used in CBOR encodings instead
format, the "aif" claim. In this memo we propose to use the compact of the string values defined in [RFC6749].
format provided by AIF [I-D.bormann-core-ace-aif]. Access rights may
be specified as a list of URIs of resources together with allowed
actions (GET, POST, PUT, PATCH, or DELETE). Other formats may be
mandated by specific applications or requirements (e.g. specifying
local conditions on access).
5.5. CBOR Data Formats /--------------------+----------+--------------\
| grant_type | CBOR Key | Major Type |
|--------------------+----------+--------------|
| password | 0 | 0 (uint) |
| authorization_code | 1 | 0 |
| client_credentials | 2 | 0 |
| refresh_token | 3 | 0 |
\--------------------+----------+--------------/
The /token resource (called "endpoint" in OAuth 2.0), defined in Figure 6: CBOR abbreviations for common grant types
Section 3.2 of [RFC6749], is used by the client to obtain an access
token. Requests sent to the /token resource use the HTTP POST method
and the payload includes a query component, which is formatted as
application/x-www-form-urlencoded. CoAP payloads cannot be formatted
in the same way which requires the /token resource on the AS to be
profiled. Appendix D defines a CBOR-based format for sending
parameters to the /token resource.
5.6. Token Expiration 6.4.2. Token Type and Algorithms
Depending on the capabilities of the RS, there are various ways in To allow clients to indicate support for specific token types and
which it can verify the validity of a received access token. We list respective algorithms they need to interact with the AS. They can
the possibilities here including what functionality they require of either provide this information out-of-band or via the 'token_type'
the RS. and 'alg' parameter in the client request.
o The token is a CWT/JWT and includes a 'exp' claim and possibly the The value in the 'alg' parameter together with value from the
'nbf' claim. The RS verifies these by comparing them to values 'token_type' parameter allow the client to indicate the supported
from its internal clock as defined in [RFC7519]. In this case the algorithms for a given token type. The token type refers to the
RS must have a real time chip (RTC) or some other way of reliably specification used by the client to interact with the resource server
measuring time. to demonstrate possession of the key. The 'alg' parameter provides
further information about the algorithm, such as whether a symmetric
or an asymmetric crypto-system is used. Hence, a client supporting a
specific token type also knows how to populate the values to the
'alg' parameter.
o The RS verifies the validity of the token by performing an This document registers the new value "pop" for the OAuth Access
introspection request as specified in Appendix D.2. This requires Token Types registry, specifying a Proof-of-Possession token. How
the RS to have a reliable network connection to the AS and to be the proof-of-possession is performed is specified by the 'alg'
able to handle two secure sessions in parallel (C to RS and AS to parameter. Profiles of this framework are responsible for defining
RS). values for the 'alg' parameter together with the corresponding proof-
of-possession mechanisms.
o The RS and the AS both store a sequence number linked to their The values in the 'alg' parameter are case-sensitive. If the client
common security association. The AS increments this number for supports more than one algorithm then each individual value MUST be
each access token it issues and includes it in the access token, separated by a space.
which is a CWT/JWT. The RS keeps track of the most recently
received sequence number, and only accepts tokens as valid, that
are in a certain range around this number. This method does only
require the RS to keep track of the sequence number. The method
does not provide timely expiration, but it makes sure that older
tokens cease to be valid after a specified number of newer ones
got issued. For a constrained RS with no network connectivity and
no means of reliably measuring time, this is the best that can be
achieved.
6. Deployment Scenarios 6.4.3. Profile
There is a large variety of IoT deployments, as is indicated in The "profile" parameter identifies the communication protocol and the
Appendix A, and this section highlights common variants. This communication security protocol between the client and the RS.
section is not normative but illustrates how the framework can be
applied.
For each of the deployment variants there are a number of possible An initial set of profile identifiers and their CBOR encodings are
security setups between clients, resource servers and authorization specified in Figure 7. Profiles using other combinations of
servers. The main focus in the following subsections is on how protocols are expected to define their own profile identifiers.
authorization of a client request for a resource hosted by a RS is
performed. This requires us to also consider how these requests and
responses between the clients and the resource servers are secured.
The security protocols between other pairs of nodes in the /--------------------+----------+--------------\
architecture, namely client-to-AS and RS-to-AS, are not detailed in | Profile identifier | CBOR Key | Major Type |
these examples. Different security protocols may be used on |--------------------+----------+--------------|
transport or application layer. | http_tls | 0 | 0 (uint) |
| coap_dtls | 1 | 0 |
| coap_oscoap | 2 | 0 |
\--------------------+----------+--------------/
Note: We use the CBOR diagnostic notation for examples of requests Figure 7: Profile identifiers and their CBOR mappings
and responses.
6.1. Client and Resource Server are Offline Profiles MAY define additional parameters for both the token request
and the client information in the access token response in order to
support negotioation or signalling of profile specific parameters.
In this scenario we consider the case where both the resource server 6.4.4. Confirmation
and the client are offline, i.e., they are not connected to the AS at
the time of the resource request. This access procedure involves
steps A, B, C, and F of Figure 1, but assumes that step A and B have
been carried out during a phase when the client had connectivity to
AS.
Since the resource server must be able to verify the access token The "cnf" parameter identifies or provides the key used for proof-of-
locally, self-contained access tokens must be used. possession. This framework extends the definition of 'cnf' from
[RFC7800] by defining CBOR/COSE encodings and the use of 'cnf' for
transporting keys in the client information.
This example shows the interactions between a client, the A CBOR encoded payload MAY contain the 'cnf' parameter with the
authorization server and a temperature sensor acting as a resource following contents:
server. Message exchanges A and B are shown in Figure 7.
A: The client first generates a public-private key pair used for COSE_Key In this case the 'cnf' parameter contains the proof-of-
communication security with the RS. possession key to be used by the client. An example is shown in
Figure 8.
The client sends the POST request to /token at AS. The request "cnf" : {
contains the public key of the client and the Audience parameter "COSE_Key" : {
set to "tempSensorInLivingRoom", a value that the temperature "kty" : "EC",
sensor identifies itself with. The AS evaluates the request and "kid" : h'11',
authorizes the client to access the resource. "crv" : "P-256",
"x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
"y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
}
}
B: The AS responds with a PoP token and client information. The Figure 8: Confirmation parameter containing a public key
PoP token contains the public key of the client, while the client
information contains the public key of the RS. For communication
security this example uses DTLS with raw public keys between the
client and the RS.
Note: In this example we assume that the client knows what COSE_Encrypted In this case the 'cnf' parameter contains an
resource it wants to access, and is therefore able to request encrypted symmetriic key destined for the client. The client is
specific audience and scope claims for the access token. assumed to be able to decrypt the cihpertext of this parameter.
The parameter is encoded as COSE_Encrypted object wrapping a
COSE_Key object. Figure 9 shows an example of this type of
encoding.
Authorization "cnf" : {
Client Server "COSE_Encrypted" : {
| | 993(
| | [ h'a1010a' # protected header : {"alg" : "AES-CCM-16-64-128"}
A: +-------->| Header: POST (Code=0.02) "iv" : b64'ifUvZaHFgJM7UmGnjA', # unprotected header
| POST | Uri-Path:"token" b64'WXThuZo6TMCaZZqi6ef/8WHTjOdGk8kNzaIhIQ' # ciphertext
| | Payload: <Request-Payload> ]
| | )
B: |<--------+ Header: 2.05 Content }
| | Content-Type: application/cbor }
| 2.05 | Payload: <Response-Payload>
| |
Figure 7: Token Request and Response Using Client Credentials. Figure 9: Confirmation paramter containing an encrypted symmetric key
The information contained in the Request-Payload and the Response- The ciphertext here could e.g. contain a symmetric key as in
Payload is shown in Figure 8. Figure 10.
Request-Payload :
{ {
"grant_type" : "client_credentials", "kty" : "Symmetric",
"aud" : "tempSensorInLivingRoom", "kid" : b64'39Gqlw',
"client_id" : "myclient", "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh'
"client_secret" : "qwerty"
} }
Response-Payload : Figure 10: Example plaintext of an encrypted cnf parameter
{
"access_token" : b64'SlAV32hkKG ...', Key Identifier In this case the 'cnf' parameter references a key
"token_type" : "pop", that is assumed to be previously known by the recipient. This
"csp" : "DTLS", allows clients that perform repeated requests for an access token
"key" : b64'eyJhbGciOiJSU0ExXzUi ...' for the same audience but e.g. with different scopes to omit key
transport in the access token, token request and token response.
Figure 11 shows such an example.
"cnf" : {
"kid" : b64'39Gqlw'
} }
Figure 8: Request and Response Payload Details. Figure 11: A Confirmation parameter with just a key identifier
The content of the "key" parameter and the access token are shown in 6.5. Mapping parameters to CBOR
Figure 9 and Figure 10.
All OAuth parameters in access token requests and responses are
mapped to CBOR types as follows and are given an integer key value to
save space.
/-------------------+----------+-----------------\
| Parameter name | CBOR Key | Major Type |
|-------------------+----------+-----------------|
| client_id | 1 | 3 (text string) |
| client_secret | 2 | 2 (byte string) |
| response_type | 3 | 3 |
| redirect_uri | 4 | 3 |
| scope | 5 | 3 |
| state | 6 | 3 |
| code | 7 | 2 |
| error_description | 8 | 3 |
| error_uri | 9 | 3 |
| grant_type | 10 | 0 (unit) |
| access_token | 11 | 3 |
| token_type | 12 | 0 |
| expires_in | 13 | 0 |
| username | 14 | 3 |
| password | 15 | 3 |
| refresh_token | 16 | 3 |
| alg | 17 | 3 |
| cnf | 18 | 5 (map) |
| aud | 19 | 3 |
| profile | 20 | 0 |
\---------------+--------------+-----------------/
Figure 12: CBOR mappings used in token requests
7. The 'Introspect' Resource
Token introspection [RFC7662] is used by the RS and potentially the
client to query the AS for metadata about a given token e.g. validity
or scope. Analogous to the protocol defined in RFC 7662 [RFC7662]
for HTTP and JSON, this section defines adaptations to more
constrained environments using CoAP and CBOR.
Communication between the RS and the introspection resource at the AS
MUST be integrity protected and encrypted. Furthermore AS and RS
MUST perform mutual authentication. Finally the AS SHOULD to verify
that the RS has the right to access introspection information about
the provided token. Profiles of this framework are expected to
specify how authentication and communication security is implemented.
The figures of this section uses CBOR diagnostic notation without the
integer abbreviations for the parameters or their values for better
readability.
7.1. RS-to-AS Request
The RS sends a CoAP POST request to the introspection resource at the
AS, with payload sent as "application/cbor" data. The payload is a
CBOR map with a 'token' parameter containing the access token along
with optional parameters representing additional context that is
known by the RS to aid the AS in its response.
The same parameters are required and optional as in section 2.1 of
RFC 7662 [RFC7662].
For example, Figure 13 shows a RS calling the token introspection
resource at the AS to query about an OAuth 2.0 proof-of-possession
token.
Header: POST (Code=0.02)
Uri-Host: "server.example.com"
Uri-Path: "introspect"
Content-Type: "application/cbor"
Payload:
{ {
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk', "token" : b64'7gj0dXJQ43U',
"kty" : "EC", "token_type_hint" : "pop"
"crv" : "P-256",
"x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4',
"y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM'
} }
Figure 9: Public Key of the RS. Figure 13: Example introspection request.
7.2. AS-to-RS Response
The AS responds with a CBOR object in "application/cbor" format with
the same required and optional parameters as in section 2.2. of RFC
7662 [RFC7662] with the following additions:
alg
OPTIONAL. See Section 6.4 for more details.
cnf
OPTIONAL. This field contains information about the proof-of-
possession key that binds the client to the access token. See
Section 6.4 for more details on the formatting of the 'cnf'
parameter.
profile
OPTIONAL. This indicates the profile that the RS MUST use with
the client. See Section 6.4 for more details on the formatting of
this parameter.
client_token
OPTIONAL. This parameter contains information that the RS MUST
pass on to the client. See Section 7.4 for more details.
For example, Figure 14 shows an AS response to the introspection
request in Figure 13.
Header: Created Code=2.01)
Content-Type: "application/cbor"
Payload:
{ {
"aud" : "tempSensorInLivingRoom", "active" : true,
"iat" : "1360189224", "scope" : "read",
"token_type" : "pop",
"alg" : "HS256",
"profile" : "coap_dtls",
"client_token" : b64'2QPhg0OhAQo ...
(remainder of client token omitted for brevity)',
"cnf" : { "cnf" : {
"jwk" : { "COSE_Key" : {
"kid" : b64'1Bg8vub9tLe1gHMzV76e8', "kty" : "Symmetric",
"kty" : "EC", "kid" : b64'39Gqlw',
"crv" : "P-256", "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh'
"x" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU',
"y" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0'
} }
} }
} }
Figure 10: Access Token including Public Key of the Client. Figure 14: Example introspection response.
Messages C and F are shown in Figure 11 - Figure 12. 7.3. Error Response
C: The client then sends the PoP token to the /authz-info resource The error responses for CoAP-based interactions with the AS are
at the RS. This is a plain CoAP request, i.e. no DTLS/OSCOAP equivalent to the ones for HTTP-based interactions as defined in
between client and RS, since the token is integrity protected section 2.3 of [RFC7662], with the following differences:
between AS and RS. The RS verifies that the PoP token was created
by a known and trusted AS, is valid, and responds to the client.
The RS caches the security context together with authorization
information about this client contained in the PoP token.
The client and resource server run the DTLS handshake using the o If content is sent, the Content-Type MUST be set to "application/
raw public keys established in step B and C. cbor", and the payload MUST be encoded in a CBOR map.
o If the credentials used by the RS are invalid the AS MUST respond
with the CoAP response code code 4.01 (Unauthorized) and use the
required and optional parameters from section 5.2 in RFC 6749
[RFC6749].
o If the RS does not have the right to perform this introspection
request, the AS MUST respond with the CoAP response code 4.03
(Forbidden). In this case no payload is returned.
The client sends the CoAP request GET to /temperature on RS over Note that a properly formed and authorized query for an inactive or
DTLS. The RS verifies that the request is authorized. otherwise invalid token does not warrant an error response by this
specification. In these cases, the authorization server MUST instead
respond with an introspection response with the "active" field set to
"false".
F: The RS responds with a resource representation over DTLS. 7.4. Client Token
Resource EDITORIAL NOTE: We have tentatively introduced this concept and would
Client Server specifically like feedback if this is viewed as a useful addition to
| | the framework.
C: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"authz-info"
| | Payload: SlAV32hkKG ...
| | (access token)
| |
|<--------+ Header: 2.04 Changed
| 2.04 |
| |
Figure 11: Access Token provisioning to RS In cases where the client has limited connectivity and is requesting
access to a previously unknown resource servers, using a long term
token, there are situations where it would be beneficial to relay the
proof-of-possession key and other relevant information from the AS to
the client through the RS. The client_token parameter is designed to
carry such information, and is intended to be used as described in
Figure 15.
Resource Resource Authorization
Client Server Client Server Server
| | | | |
|<=======>| DTLS Connection Establishment | | |
| | using Raw Public Keys A: +--------------->| |
| | | POST | |
| | | Access Token | |
+-------->| Header: GET (Code=0.01) | B: +--------------->|
| GET | Uri-Path: "temperature" | | Introspection |
| | | | Request |
| | | | |
| | | C: +<---------------+
F: |<--------+ Header: 2.05 Content | | Introspection |
| 2.05 | Payload: {"t":"22.7"} | | Response |
| | | | + Client Token |
D: |<---------------+ |
| 2.01 Created | |
| + Client Token |
Figure 12: Resource Request and Response protected by DTLS. Figure 15: Use of the client_token parameter.
6.2. Resource Server Offline The client token is a COSE_Encrytped object, containing as payload a
CBOR map with the following claims:
In this deployment scenario we consider the case of an RS that may cnf
not be able to access the AS at the time it receives an access REQUIRED. Contains information about the proof-of-possession key
request from a client. We denote this case "RS offline", it involves the client is to use with its access token. See Section 6.4.4.
steps A, B, C and F of Figure 1.
If the RS is offline, then it must be possible for the RS to locally token_type
validate the access token. This requires self-contained tokens to be OPTIONAL. See Section 6.4.2.
used.
The validity time for the token should always be chosen as short as alg
possible to reduce the possibility that a token contains out-of-date OPTIONAL. See Section 6.4.2.
authorization information. Therefore the value for the Expiration
Time claim ("exp") should be set only slightly larger than the value
for the Issuing Time claim ("iss"). A constrained RS with means to
reliably measure time must validate the expiration time of the access
token.
The following example shows interactions between a client (air- profile
conditioning control unit), an offline resource server (temperature REQUIRED. See Section 6.4.3.
sensor)and an authorization server. The message exchanges A and B
are shown in Figure 13.
A: The client sends the request POST to /token at AS. The request rs_cnf
contains the Audience parameter set to "tempSensor109797", a value OPTIONAL. Contains information about the key that the RS uses to
that the temperature sensor identifies itself with. The scope the authenticate towards the client. If the key is symmetric then
client wants the AS to authorize the access token for is "owner", this claim MUST NOT be part of the Client Token, since this is the
which means that the token can be used to both read temperature same key as the one specified through the 'cnf' claim. This claim
data and upgrade the firmware on the RS. The AS evaluates the uses the same encoding as the 'cnf' parameter. See Section 6.4.3.
request and authorizes the client to access the resource.
B: The AS responds with a PoP token and client information. The The AS encrypts this token using a key shared between the AS and the
PoP token is wrapped in a COSE message, object secured content client, so that only the client can decrypt it and access its
from AS to RS. The client information contains a symmetric key. payload. How this key is established is out of scope of this
In this case communication security between C and RS is OSCOAP framework.
with an authenticated encryption algorithm. The client derives
two unidirectional security contexts to use with the resource
request and response messages. The access token includes the
claim "aif" with the authorized access that an owner of the
temperature device can enjoy. The "aif" claim, issued by the AS,
informs the RS that the owner of the access token, that can prove
the possession of a key is authorized to make a GET request
against the /tempC resource and a POST request on the /firmware
resource.
Authorization 7.5. Mapping Introspection parameters to CBOR
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path: "token"
| | Payload: <Request-Payload>
| |
B: |<--------+ Header: 2.05 Content
| | Content-Type: application/cbor
| 2.05 | Payload: <Response-Payload>
| |
| |
Figure 13: Token Request and Response The introspection request and response parameters are mapped to CBOR
types as follows and are given an integer key value to save space.
The information contained in the Request-Payload and the Response- /----------------+----------+-----------------\
Payload is shown in Figure 14. | Parameter name | CBOR Key | Major Type |
|----------------+----------+-----------------|
| active | 1 | 0 (uint) |
| username | 2 | 3 (text string) |
| client_id | 3 | 3 |
| scope | 4 | 3 |
| token_type | 5 | 3 |
| exp | 6 | 6 tag value 1 |
| iat | 7 | 6 tag value 1 |
| nbf | 8 | 6 tag value 1 |
| sub | 9 | 3 |
| aud | 10 | 3 |
| iss | 11 | 3 |
| jti | 12 | 3 |
| alg | 13 | 3 |
| cnf | 14 | 5 (map) |
| aud | 15 | 3 |
| client_token | 16 | 3 |
| rs_cnf | 17 | 5 |
\----------------+----------+-----------------/
Request-Payload: Figure 16: CBOR Mappings to Token Introspection Parameters.
{
"grant_type" : "client_credentials",
"client_id" : "myclient",
"client_secret" : "qwerty",
"aud" : "tempSensor109797",
"scope" : "owner"
}
Response-Payload: 8. The Access Token
{
"access_token": b64'SlAV32hkKG ...',
"token_type" : "pop",
"csp" : "OSCOAP",
"key" : b64'eyJhbGciOiJSU0ExXzUi ...'
}
Figure 14: Request and Response Payload for RS offline This framework RECOMMENDS the use of CBOR web token (CWT) as
specified in [I-D.ietf-ace-cbor-web-token].
Figure 15 shows examples of the key and the access_token parameters In order to facilitate offline processing of access tokens, this
of the Response-Payload, decoded to CBOR. draft specfifies the "scope" claim for access tokens that explicitly
encodes the scope of a given access token. This claim follows the
same encoding rules as defined in section 3.3 of [RFC6749]. The
meaning of a specific scope value is application specific and
expected to be known to the RS running that application.
access_token: 8.1. The 'Authorization Information' Resource
{
"aud" : "tempSensor109797",
"exp" : 1311281970,
"iat" : 1311280970,
"aif" : [["/tempC", 0], ["/firmware", 2]],
"cnf" : {
"ck":b64'JDLUhTMjU2IiwiY3R5Ijoi ...'
}
}
key: The access token, containing authorization information and
{ information of the key used by the client, is transported to the RS
"alg" : "AES_128_CCM_8", so that the RS can authenticate and authorize the client request.
"kid" : b64'U29tZSBLZXkgSWQ', This section defines a method for transporting the access token to
"k" : b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE' the RS using CoAP that MAY be used. An ACE profile MAY define other
} methods for token transport.
Figure 15: Access Token and symmetric key from the Response-Payload This method REQUIRES the RS to implement an /authz-info resource. A
client using this method MUST make a POST request to /authz-info on
the RS with the access token in the payload. The RS receiving the
token MUST verify the validity of the token. If the token is valid,
the RS MUST respond to the POST request with 2.04 (Changed).
Message exchanges C and F are shown in Figure 16 and Figure 17. If the token is not valid, the RS MUST respond with error code 4.01
(Unauthorized). If the token is valid but the audience of the token
does not match the RS, the RS MUST respond with error code 4.03
(Forbidden).
C: The client then sends the PoP token to the /authz-info resource The RS MAY make an introspection request to validate the token before
in the RS. This is a plain CoAP request, i.e. no DTLS/OSCOAP responding to the POST /authz-info request. If the introspection
between client and RS, since the token is integrity protected response contains a client token (Section 7.4) then this token SHALL
between AS and RS. The RS verifies that the PoP token was created be included in the payload of the 2.04 (Changed) response.
by a known and trusted AS, is valid, and responds to the client.
The RS derives and caches the security contexts together with
authorization information about this client contained in the PoP
token.
The client sends the CoAP requests GET to /tempC on the RS using 8.2. Token Expiration
OSCOAP. The RS verifies the request and that it is authorized.
F: The RS responds with a protected status code using OSCOAP. The Depending on the capabilities of the RS, there are various ways in
client verifies the response. which it can verify the validity of a received access token. We list
the possibilities here including what functionality they require of
the RS.
Resource o The token is a CWT/JWT and includes a 'exp' claim and possibly the
Client Server 'nbf' claim. The RS verifies these by comparing them to values
| | from its internal clock as defined in [RFC7519]. In this case the
C: +-------->| Header: POST (Code=0.02) RS must have a real time chip (RTC) or some other way of reliably
| POST | Uri-Path:"authz-info" measuring time.
| | Payload: <Access Token> o The RS verifies the validity of the token by performing an
| | introspection request as specified in Section 7. This requires
| | the RS to have a reliable network connection to the AS and to be
|<--------+ Header: 2.04 Changed able to handle two secure sessions in parallel (C to RS and AS to
| 2.04 | RS).
| | o The RS and the AS both store a sequence number linked to their
| | common security association. The AS increments this number for
each access token it issues and includes it in the access token,
which is a CWT/JWT. The RS keeps track of the most recently
received sequence number, and only accepts tokens as valid, that
are in a certain range around this number. This method does only
require the RS to keep track of the sequence number. The method
does not provide timely expiration, but it makes sure that older
tokens cease to be valid after a certain number of newer ones got
issued. For a constrained RS with no network connectivity and no
means of reliably measuring time, this is the best that can be
achieved.
Figure 16: Access Token provisioning to RS 9. Security Considerations
Resource The entire document is about security. Security considerations
Client Server applicable to authentication and authorization in RESTful
| | environments provided in OAuth 2.0 [RFC6749] apply to this work, as
+-------->| Header: GET (Code=0.01) well as the security considerations from [I-D.ietf-ace-actors].
| GET | Object-Security: Furthermore [RFC6819] provides additional security considerations for
| | (<seq>,<cid>,[Uri-Path:"tempC"],<tag>) OAuth which apply to IoT deployments as well. Finally
| | [I-D.ietf-oauth-pop-architecture] discusses security and privacy
F: |<--------+ Header: 2.05 Content threats as well as mitigation measures for Proof-of-Possession
| 2.05 | Object-Security: tokens.
| | (<seq>,<cid>,[22.7 C],<tag>)
| |
Figure 17: Resource request and response protected by OSCOAP 10. IANA Considerations
In Figure 17 the GET request contains an Object-Security option and This specification registers new parameters for OAuth and establishes
an indication of the content of the COSE object: a sequence number registries for mappings to CBOR.
("seq", starting from 0), a context identifier ("cid") indicating the
security context, the ciphertext containing the encrypted CoAP option
identifying the resource, and the Message Authentication Code ("tag")
which also covers the Code in the CoAP header.
The Object-Security ciphertext in the response [22.7 C] represents an 10.1. OAuth Introspection Response Parameter Registration
encrypted temperature reading. (The COSE object is actually carried
in the CoAP payload when possible but that is omitted to simplify
notation.)
6.3. Token Introspection with an Offline Client This specification registers the following parameters in the OAuth
introspection response parameters
In this deployment scenario we assume that a client is not be able to o Name: "alg"
access the AS at the time of the access request. Since the RS is, o Description: Algorithm to use with PoP key, as defined in PoP
however, connected to the back-end infrastructure it can make use of token specification,
token introspection. This access procedure involves steps A-F of o Change Controller: IESG
Figure 1, but assumes steps A and B have been carried out during a o Specification Document(s): this document
phase when the client had connectivity to AS.
Since the client is assumed to be offline, at least for a certain o Name: "cnf"
period of time, a pre-provisioned access token has to be long-lived. o Description: Key to use to prove the right to use an access token,
The resource server may use its online connectivity to validate the as defined in [RFC7800].
access token with the authorization server, which is shown in the o Change Controller: IESG
example below. o Specification Document(s): this document
In the example we show the interactions between an offline client o Name: "aud"
(key fob), a resource server (online lock), and an authorization o Description: reference to intended receiving RS, as defined in PoP
server. We assume that there is a provisioning step where the client token specification.
has access to the AS. This corresponds to message exchanges A and B o Change Controller: IESG
which are shown in Figure 18. o Specification Document(s): this document
A: The client sends the request using POST to /token at AS. The o Name: "profile"
request contains the Audience parameter set to "lockOfDoor4711", a o Description: The communication and communication security profile
value the that the online door in question identifies itself with. used between client and RS, as defined in ACE profiles.
The AS generates an access token as on opaque string, which it can o Change Controller: IESG
match to the specific client, a targeted audience and a symmetric o Specification Document(s): this document
key security context.
B: The AS responds with the an access token and client o Name: "client_token"
information, the latter containing a symmetric key. Communication o Description: Information that the RS MUST pass to the client e.g.
security between C and RS will be OSCOAP with authenticated about the proof-of-possession keys.
encryption. o Change Controller: IESG
o Specification Document(s): this document
Authorization 10.2. OAuth Parameter Registration
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"token"
| | Payload: <Request-Payload>
| |
B: |<--------+ Header: 2.05 Content
| | Content-Type: application/cbor
| 2.05 | Payload: <Response-Payload>
| |
Figure 18: Token Request and Response using Client Credentials. This specification registers the following parameters in the OAuth
Parameters Registry
Authorization consent from the resource owner can be pre-configured, o Name: "alg"
but it can also be provided via an interactive flow with the resource o Description: Algorithm to use with PoP key, as defined in PoP
owner. An example of this for the key fob case could be that the token specification,
resource owner has a connected car, he buys a generic key that he o Change Controller: IESG
wants to use with the car. To authorize the key fob he connects it o Specification Document(s): this document
to his computer that then provides the UI for the device. After that
OAuth 2.0 implicit flow is used to authorize the key for his car at
the the car manufacturers AS.
The information contained in the Request-Payload and the Response- o Parameter name: "profile"
Payload is shown in Figure 19. o Parameter usage location: token request, and token response
o Change Controller: IESG
o Specification Document(s): this document
Request-Payload: o Name: "cnf"
{ o Description: Key to use to prove the right to use an access token,
"grant_type" : "token", as defined in [RFC7800].
"aud" : "lockOfDoor4711", o Change Controller: IESG
"client_id" : "myclient", o Specification Document(s): this document
}
Response-Payload: 10.3. OAuth Access Token Types
{
"access_token" : b64'SlAV32hkKG ...'
"token_type" : "pop",
"csp" : "OSCOAP",
"key" : b64'eyJhbGciOiJSU0ExXzUi ...'
}
Figure 19: Request and Response Payload for C offline This specification registers the following new token type in the
OAuth Access Token Types Registry
The access token in this case is just an opaque string referencing o Name: "PoP"
the authorization information at the AS. o Description: A proof-of-possession token.
o Change Controller: IESG
o Specification Document(s): this document
C: Next, the client POSTs the access token to the /authz-info 10.4. Token Type Mappings
resource in the RS. This is a plain CoAP request, i.e. no DTLS/
OSCOAP between client and RS. Since the token is an opaque
string, the RS cannot verify it on its own, and thus defers to
respond the client with a status code until step E and only
acknowledges on the CoAP message layer (indicated with a dashed
line).
Resource A new registry will be requested from IANA, entitled "Token Type
Client Server Mappings". The registry is to be created as Expert Review Required.
| |
C: +-------->| Header: POST (T=CON, Code=0.02
| POST | Token 0x2a12)
| | Uri-Path:"authz-info"
| | Payload: SlAV32hkKG ...
| | (access token)
| |
|<- - - - + Header: T=ACK
| |
Figure 20: Access Token provisioning to RS 10.4.1. Registration Template
D: The RS forwards the token to the /introspect resource on the Token Type:
AS. Introspection assumes a secure connection between the AS and Name of token type as registered in the OAuth token type registry
the RS, e.g. using DTLS or OSCOAP, which is not detailed in this e.g. "Bearer".
example. Mapped value:
Integer representation for the token type value. The key value
MUST be an integer in the range of 1 to 65536.
Change Controller:
E: The AS provides the introspection response containing claims For Standards Track RFCs, list the "IESG". For others, give the
about the token. This includes the confirmation key (cnf) claim name of the responsible party. Other details (e.g., postal
that allows the RS to verify the client's proof of possession in address, email address, home page URI) may also be included.
step F. Specification Document(s):
Reference to the document or documents that specify the
parameter,preferably including URIs that can be used to retrieve
copies of the documents. An indication of the relevant sections
may also be included but is not required.
After receiving message E, the RS responds to the client's POST in 10.4.2. Initial Registry Contents
step C with Code 2.04 (Changed), using CoAP Token 0x2a12. This
step is not shown in the figures.
Resource Authorization o Parameter name: "Bearer"
Server Server o Mapped value: 1
| | o Change Controller: IESG
D: +--------->| Header: POST (Code=0.02) o Specification Document(s): this document
| POST | Uri-Path: "introspect"
| | Payload: <Request-Payload>
| |
E: |<---------+ Header: 2.05 Content
| 2.05 | Content-Type: application/cbor)
| | Payload: <Response-Payload>
| |
Figure 21: Token Introspection for C offline o Parameter name: "pop"
o Mapped value: 2
o Change Controller: IESG
o Specification Document(s): this document
The information contained in the Request-Payload and the Response- 10.5. JSON Web Token Claims
Payload is shown in Figure 22.
Request-Payload: This specification registers the following new claim in the JSON Web
{ Token (JWT) registry.
"token" : b64'SlAV32hkKG...',
"client_id" : "myRS",
"client_secret" : "ytrewq"
}
Response-Payload: o Claim Name: "scope"
{ o Claim Description: The scope of an access token as defined in
"active" : true, [RFC6749].
"aud" : "lockOfDoor4711", o Change Controller: IESG
"scope" : "open, close", o Specification Document(s): this document
"iat" : 1311280970,
"cnf" : {
"ck" : b64'JDLUhTMjU2IiwiY3R5Ijoi ...'
}
}
Figure 22: Request and Response Payload for Introspection 10.6. ACE Profile Registry
The client sends the CoAP requests PUT 1 (= "close the lock") to A new registry will be requested from IANA, entitled "ACE Profile
/lock on RS using OSCOAP with a security context derived from the Registry". The registry is to be created as Expert Review Required.
key supplied in step B. The RS verifies the request with the key
supplied in step E and that it is authorized by the token supplied
in step C.
F: The RS responds with a protected status code using OSCOAP. The 10.6.1. Registration Template
client verifies the response.
Resource Profile name:
Client Server Name of the profile to be included in the profile attribute.
| | Profile description:
+-------->| Header: PUT (Code=0.03) Text giving an over view of the profile and the context it is
| PUT | Object-Security: developed for.
| | (<seq>,<cid>,[Uri-Path:"lock", 1],<tag>) Profile ID:
| | Integer value to identify the profile. The value MUST be an
F: |<--------+ Header: 2.04 Changed integer in the range of 1 to 65536.
| 2.04 | Object-Security: Change Controller:
| | (<seq>,<cid>,,<tag>)
| |
Figure 23: Resource request and response protected by OSCOAP For Standards Track RFCs, list the "IESG". For others, give the
name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the
parameter,preferably including URIs that can be used to retrieve
copies of the documents. An indication of the relevant sections
may also be included but is not required.
The Object-Security ciphertext [...] of the PUT request contains CoAP 10.7. OAuth Parameter Mappings Registry
options that are encrypted, as well as the payload value '1' which is
the value of PUT to the door lock.
In this example there is no ciphertext of the PUT response, but "tag" A new registry will be requested from IANA, entitled "Token Resource
contains a MAC which covers the request sequence number and context CBOR Mappings Registry". The registry is to be created as Expert
identifier as well as the Code which allows the Client to verify that Review Required.
this actuator command was well received (door is locked).
6.4. Always-On Connectivity 10.7.1. Registration Template
A popular deployment scenario for IoT devices is to have them always Parameter name:
be connected to the Internet so that they can be reachable to receive OAuth Parameter name, refers to the name in the OAuth parameter
commands. As a continuation from the previous scenarios we assume registry e.g. "client_id".
that both the client and the RS are online at the time of the access CBOR key value:
request. Key value for the claim. The key value MUST be an integer in the
range of 1 to 65536.
Change Controller:
For Standards Track RFCs, list the "IESG". For others, give the
name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the
parameter,preferably including URIs that can be used to retrieve
copies of the documents. An indication of the relevant sections
may also be included but is not required.
If the client and the resource server are online then the AS should 10.7.2. Initial Registry Contents
be configured to issue short-lived access tokens for the resource to
the client. The resource server must then validate self-contained
access tokens or otherwise must use token introspection to obtain the
up-to-date claim information. If transmission costs are high or the
channel is lossy, the CWT token format
[I-D.wahlstroem-ace-cbor-web-token] may be used instead of a JWT to
reduce the volume of network traffic. In terms of messaging this
deployment scenario uses the patterns described in the previous sub-
sections.
Note that despite the lack of connectivity constraints there may o Parameter name: "client_id"
still be other restrictions a deployment may face. o CBOR key value: 1
o Change Controller: IESG
o Specification Document(s): this document
6.5. Token-less Authorization o Parameter name: "client_secret"
o CBOR key value: 2
o Change Controller: IESG
o Specification Document(s): this document
In this deployment scenario we consider the case of an RS which is o Parameter name: "response_type"
severely energy constrained, sleeps most of the time and need to have o CBOR key value: 3
a tight messaging budget. It is not only infeasible to access the AS o Change Controller: IESG
at the time of the access request, as in the "RS offline" case o Specification Document(s): this document
Section 6.2, it must be offloaded as much message communication as
possible.
OAuth 2.0 is already an efficient protocol in terms of message o Parameter name: "redirect_uri"
exchanges and can be further optimized by compact encodings of o CBOR key value: 4
tokens. The scenario illustrated in this section goes beyond that o Change Controller: IESG
and removes the access tokens from the protocol. This may be o Specification Document(s): this document
considered a degenerate case of OAuth 2.0 but it allows us to do two
things:
1. The common case where authorization is performed by means of o Parameter name: "scope"
authentication fits into the same protocol framework. o CBOR key value: 5
Authentication protocol and key is specified by client o Change Controller: IESG
information, and access token is omitted. o Specification Document(s): this document
2. Authentication, and thereby authorization, may even be implicit, o Parameter name: "state"
i.e. anyone with access to the right key is authorized to access o CBOR key value: 6
the protected resource. o Change Controller: IESG
o Specification Document(s): this document
In case 2., the RS does not need to receive any message from the o Parameter name: "code"
client, and therefore enables offloading recurring resource request o CBOR key value: 7
and response processing to a third party, such as a Message Broker o Change Controller: IESG
(MB) in a publish-subscribe setting. o Specification Document(s): this document
This scenario involves steps A, B, C and F of Figure 1 and four o Parameter name: "error_description"
parties: a client (subscriber), an offline RS (publisher), a trusted o CBOR key value: 8
AS, and a MB, not necessarily trusted with access to the plain text o Change Controller: IESG
publications. Message exchange A, B is shown in Figure 24. o Specification Document(s): this document
A: The client sends the request POST to /token at AS. The request o Parameter name: "error_uri"
contains the Audience parameter set to "birchPollenSensor301", a o CBOR key value: 9
value that characterizes a certain pollen sensor resource. The AS o Change Controller: IESG
evaluates the request and authorizes the client to access the o Specification Document(s): this document
resource.
B: The AS responds with an empty token and client information with o Parameter name: "grant_type"
a security context to be used by the client. The empty token o CBOR key value: 10
signifies that authorization is performed by means of o Change Controller: IESG
authentication using the communication security protocol indicated o Specification Document(s): this document
with "csp". In this case it is object security of content (OSCON)
i.e. protection of CoAP payload only. The security context
contains the symmetric decryption key and a public signature
verification key of the RS.
Authorization o Parameter name: "access_token"
Client Server o CBOR key value: 11
| | o Change Controller: IESG
| | o Specification Document(s): this document
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"token"
| | Payload: <Request-Payload>
| |
B: |<--------+ Header: 2.05 Content
| | Content-Type: application/cbor
| 2.05 | Payload: <Response-Payload>
| |
| |
Figure 24: Token Request and Response o Parameter name: "token_type"
o CBOR key value: 12
o Change Controller: IESG
o Specification Document(s): this document
The information contained in the Request-Payload and the Response- o Parameter name: "expires_in"
Payload is shown in Figure 25. o CBOR key value: 13
o Change Controller: IESG
o Specification Document(s): this document
Request-Payload : o Parameter name: "username"
{ o CBOR key value: 14
"grant_type" : "client_credentials", o Change Controller: IESG
"aud" : "birchPollenSensor301", o Specification Document(s): this document
"client_id" : "myclient",
"client_secret" : "qwerty"
}
Response-Payload : o Parameter name: "password"
{ o CBOR key value: 15
"access_token" : NULL, o Change Controller: IESG
"token_type" : "none", o Specification Document(s): this document
"csp" : "OSCON",
"key" : b64'eyJhbGciOiJSU0ExXzUi ...'
}
Figure 25: Request and Response Payload for RS severely constrained o Parameter name: "refresh_token"
o CBOR key value: 16
o Change Controller: IESG
o Specification Document(s): this document
The content of the "key" parameter is shown in Figure 26. o Parameter name: "alg"
o CBOR key value: 17
o Change Controller: IESG
o Specification Document(s): this document
key : o Parameter name: "cnf"
{ o CBOR key value: 18
"alg" : "AES_128_CTR_ECDSA", o Change Controller: IESG
"kid" : b64'c29tZSBvdGhlciBrZXkgaWQ'; o Specification Document(s): this document
"k" : b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE',
"crv" : "P-256",
"x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4',
"y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM'
}
Figure 26: The 'key' Parameter o Parameter name: "aud"
o CBOR key value: 19
o Change Controller: IESG
o Specification Document(s): this document
The RS, which sleeps most of the time, occasionally wakes up, o Parameter name: "profile"
measures the number birch pollens per cubic meters, publishes the o CBOR key value: 20
measurements to the MB, and then returns to sleep. See Figure 27. o Change Controller: IESG
o Specification Document(s): this document
In this case the birch pollen count stopped at 270, which is 10.8. Introspection Resource CBOR Mappings Registry
encrypted with the symmetric key and signed with the private key of
the RS. The MB verifies that the message originates from RS using
the public key of RS, that it is not a replay of an old measurement
using the sequence number of the OSCON COSE profile, and caches the
object secured content. The MB does not have the secret key so is
unable to read the plain text measurement.
Message exchanges C and F are shown in Figure 27. A new registry will be requested from IANA, entitled "Introspection
Resource CBOR Mappings Registry". The registry is to be created as
Expert Review Required.
C: Since there is no access token, the client does not address the 10.8.1. Registration Template
/authz-info resource in the RS. The client sends the CoAP request
GET to /birchPollen on MB which is a plain CoAP request.
F: The MB responds with the cached object secured content. Response parameter name:
Name of the response parameter as defined in the "OAuth Token
Introspection Response" registry e.g. "active".
CBOR key value:
Key value for the claim. The key value MUST be an integer in the
range of 1 to 65536.
Change Controller:
For Standards Track RFCs, list the "IESG". For others, give the
name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the
parameter,preferably including URIs that can be used to retrieve
copies of the documents. An indication of the relevant sections
may also be included but is not required.
Message Resource 10.8.2. Initial Registry Contents
Client Broker Server
| | |
| |<--------| Header: PUT (Code=0.02)
| | PUT | Uri-Path: "birchPollen"
| | | Payload: (<seq>,<cid>,["270"],<tag>)
| | |
| |-------->| Header: 2.04 Changed
| | 2.04 |
| |
| |
C: +-------->| Header: GET (Code=0.01)
| GET | Uri-Path: "birchPollen"
| |
| |
F: |<--------+ Header: 2.05 Content
| 2.05 | Payload: (<seq>,<cid>,["270"],<tag>)
| |
Figure 27: Sensor measurement protected by COSE o Response parameter name: "active"
o CBOR key value: 1
o Change Controller: IESG
o Specification Document(s): this document
The payload is a COSE message consisting of sequence number 'seq' o Response parameter name: "username"
stepped by the RS for each publication, the context identifier 'cid' o CBOR key value: 2
in this case coinciding with the key identifier 'kid' of Figure 26, o Change Controller: IESG
the encrypted measurement and the signature by the RS. o Specification Document(s): this document
Note that the same COSE message format may be used as in OSCOAP but o Response parameter name: "client_id"
that only CoAP payload is protected in this case. o CBOR key value: 3
o Change Controller: IESG
o Specification Document(s): this document
The authorization step is implicit, so while any client could request o Response parameter name: "scope"
access the COSE object, only authorized clients have access to the o CBOR key value: 4
symmetric key needed to decrypt the content. o Change Controller: IESG
o Specification Document(s): this document
Note that in this case the order of the message exchanges A,B and C,F o Response parameter name: "token_type"
could in principle be interchanged, i.e. the client could first o CBOR key value: 5
request and obtain the protected resource in steps C,F; and after o Change Controller: IESG
that request client information containing the keys decrypt and o Specification Document(s): this document
verify the message.
6.6. Securing Group Communication o Response parameter name: "exp"
o CBOR key value: 6
o Change Controller: IESG
o Specification Document(s): this document
There are use cases that require securing communication between a o Response parameter name: "iat"
(group of) senders and a group of receivers. One prominent example o CBOR key value: 7
is lighting. Often, a set of lighting nodes (e.g., luminaires, wall- o Change Controller: IESG
switches, sensors) are grouped together and only authorized members o Specification Document(s): this document
of the group must be able read and process messages. Additionally,
receivers of group messages must be able to verify the integrity of
received messages as being generated within the group.
The requirements for securely communicating in such group use cases o Response parameter name: "nbf"
efficiently is outlined in [I-D.somaraju-ace-multicast] along with an o CBOR key value: 8
architectural description that aligns with the content of this o Change Controller: IESG
document. The requirements for conveying the necessary identifiers o Specification Document(s): this document
to reference groups and also the process of commissioning devices can
be accomplished using the protocol described in this document. For
details about the lighting-unique use case aspects, the architecture,
as well as other multicast-specific considerations we refer the
reader to [I-D.somaraju-ace-multicast].
7. Security Considerations o Response parameter name: "sub"
o CBOR key value: 9
o Change Controller: IESG
o Specification Document(s): this document
The entire document is about security. Security considerations o Response parameter name: "aud"
applicable to authentication and authorization in RESTful o CBOR key value: 10
environments provided in OAuth 2.0 [RFC6749] apply to this work, as o Change Controller: IESG
well as the security considerations from [I-D.ietf-ace-actors]. o Specification Document(s): this document
Furthermore [RFC6819] provides additional security considerations for
OAuth which apply to IoT deployments as well. Finally
[I-D.ietf-oauth-pop-architecture] discusses security and privacy
threats as well as mitigation measures for Proof-of-Possession
tokens.
8. IANA Considerations o Response parameter name: "iss"
o CBOR key value: 11
o Change Controller: IESG
o Specification Document(s): this document
TBD o Response parameter name: "jti"
o CBOR key value: 12
o Change Controller: IESG
o Specification Document(s): this document
FIXME: Add registry over 'csp' values from Figure 2 o Parameter name: "alg"
o CBOR key value: 13
o Change Controller: IESG
o Specification Document(s): this document
FIXME: Add registry of 'rpk' parameter from section 5.1 o Parameter name: "cnf"
o CBOR key value: 14
o Change Controller: IESG
o Specification Document(s): this document
FIXME: Add registry of 'tktn' values from Figure 3 o Parameter name: "aud"
o CBOR key value: 15
o Change Controller: IESG
o Specification Document(s): this document
8.1. CoAP Option Number Registration 10.9. CoAP Option Number Registration
This section registers the "Access-Token" CoAP Option Number This section registers the "Access-Token" CoAP Option Number in the
[RFC2046] in "CoRE Parameters" sub-registry "CoAP Option Numbers" in "CoRE Parameters" sub-registry "CoAP Option Numbers" in the manner
the manner described in [RFC7252]. described in [RFC7252].
Name Name
Access-Token Access-Token
Number Number
TBD TBD
Reference Reference
[draft-ietf-ace-oauth-authz] [This document].
Meaning in Request Meaning in Request
Contains an Access Token according to [draft-ietf-ace-oauth-authz] Contains an Access Token according to [This document] containing
containing access permissions of the client. access permissions of the client.
Meaning in Response Meaning in Response
Not used in response Not used in response
Safe-to-Forward Safe-to-Forward
TBD TBD
Format Format
Based on the observer the format is perseved differently. Opaque Based on the observer the format is perceived differently. Opaque
data to the client and CWT or reference token to the RS. data to the client and CWT or reference token to the RS.
Length Length
Less then 255 bytes Less then 255 bytes
9. Acknowledgments 11. Acknowledgments
We would like to thank Eve Maler for her contributions to the use of We would like to thank Eve Maler for her contributions to the use of
OAuth 2.0 and UMA in IoT scenarios, Robert Taylor for his discussion OAuth 2.0 and UMA in IoT scenarios, Robert Taylor for his discussion
input, and Malisa Vucinic for his input on the ACRE proposal input, and Malisa Vucinic for his input on the ACRE proposal
[I-D.seitz-ace-core-authz] which was one source of inspiration for [I-D.seitz-ace-core-authz] which was one source of inspiration for
this work. Finally, we would like to thank the ACE working group in this work. Finally, we would like to thank the ACE working group in
general for their feedback. general for their feedback.
10. References Ludwig Seitz and Goeran Selander worked on this document as part of
the CelticPlus project CyberWI, with funding from Vinnova.
10.1. Normative References 12. References
[I-D.bormann-core-ace-aif] 12.1. Normative References
Bormann, C., "An Authorization Information Format (AIF)
for ACE", draft-bormann-core-ace-aif-03 (work in [I-D.ietf-ace-cbor-web-token]
progress), July 2015. Wahlstroem, E., Jones, M., and H. Tschofenig, "CBOR Web
Token (CWT)", draft-ietf-ace-cbor-web-token-00 (work in
progress), May 2016.
[I-D.ietf-cose-msg] [I-D.ietf-cose-msg]
Schaad, J., "CBOR Encoded Message Syntax", draft-ietf- Schaad, J., "CBOR Encoded Message Syntax", draft-ietf-
cose-msg-10 (work in progress), February 2016. cose-msg-12 (work in progress), May 2016.
[I-D.ietf-oauth-introspection]
Richer, J., "OAuth 2.0 Token Introspection", draft-ietf-
oauth-introspection-11 (work in progress), July 2015.
[I-D.ietf-oauth-pop-architecture]
Hunt, P., Richer, J., Mills, W., Mishra, P., and H.
Tschofenig, "OAuth 2.0 Proof-of-Possession (PoP) Security
Architecture", draft-ietf-oauth-pop-architecture-07 (work
in progress), December 2015.
[I-D.ietf-oauth-pop-key-distribution]
Bradley, J., Hunt, P., Jones, M., and H. Tschofenig,
"OAuth 2.0 Proof-of-Possession: Authorization Server to
Client Key Distribution", draft-ietf-oauth-pop-key-
distribution-02 (work in progress), October 2015.
[I-D.selander-ace-object-security] [I-D.selander-ace-object-security]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz, Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security of CoAP (OSCOAP)", draft-selander-ace- "Object Security of CoAP (OSCOAP)", draft-selander-ace-
object-security-03 (work in progress), October 2015. object-security-04 (work in progress), March 2016.
[I-D.wahlstroem-ace-cbor-web-token]
Wahlstroem, E., Jones, M., and H. Tschofenig, "CBOR Web
Token (CWT)", draft-wahlstroem-ace-cbor-web-token-00 (work
in progress), December 2015.
[I-D.wahlstroem-ace-oauth-introspection]
Wahlstroem, E., "OAuth 2.0 Introspection over the
Constrained Application Protocol (CoAP)", draft-
wahlstroem-ace-oauth-introspection-01 (work in progress),
March 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
Ciphersuites for Transport Layer Security (TLS)",
RFC 4279, DOI 10.17487/RFC4279, December 2005,
<http://www.rfc-editor.org/info/rfc4279>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>. January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014, DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>. <http://www.rfc-editor.org/info/rfc7252>.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", [RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7516, DOI 10.17487/RFC7516, May 2015, RFC 7662, DOI 10.17487/RFC7662, October 2015,
<http://www.rfc-editor.org/info/rfc7516>. <http://www.rfc-editor.org/info/rfc7662>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, [RFC7800] Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
DOI 10.17487/RFC7517, May 2015, Possession Key Semantics for JSON Web Tokens (JWTs)",
<http://www.rfc-editor.org/info/rfc7517>. RFC 7800, DOI 10.17487/RFC7800, April 2016,
<http://www.rfc-editor.org/info/rfc7800>.
10.2. Informative References 12.2. Informative References
[I-D.ietf-ace-actors] [I-D.ietf-ace-actors]
Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An
architecture for authorization in constrained architecture for authorization in constrained
environments", draft-ietf-ace-actors-02 (work in environments", draft-ietf-ace-actors-03 (work in
progress), October 2015. progress), March 2016.
[I-D.ietf-core-block] [I-D.ietf-core-block]
Bormann, C. and Z. Shelby, "Block-wise transfers in CoAP", Bormann, C. and Z. Shelby, "Block-wise transfers in CoAP",
draft-ietf-core-block-18 (work in progress), September draft-ietf-core-block-20 (work in progress), April 2016.
2015.
[I-D.ietf-oauth-pop-architecture]
Hunt, P., Richer, J., Mills, W., Mishra, P., and H.
Tschofenig, "OAuth 2.0 Proof-of-Possession (PoP) Security
Architecture", draft-ietf-oauth-pop-architecture-07 (work
in progress), December 2015.
[I-D.seitz-ace-core-authz] [I-D.seitz-ace-core-authz]
Seitz, L., Selander, G., and M. Vucinic, "Authorization Seitz, L., Selander, G., and M. Vucinic, "Authorization
for Constrained RESTful Environments", draft-seitz-ace- for Constrained RESTful Environments", draft-seitz-ace-
core-authz-00 (work in progress), June 2015. core-authz-00 (work in progress), June 2015.
[I-D.somaraju-ace-multicast]
Somaraju, A., Kumar, S., Tschofenig, H., and W. Werner,
"Security for Low-Latency Group Communication", draft-
somaraju-ace-multicast-01 (work in progress), January
2016.
[RFC4680] Santesson, S., "TLS Handshake Message for Supplemental
Data", RFC 4680, DOI 10.17487/RFC4680, October 2006,
<http://www.rfc-editor.org/info/rfc4680>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", [RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<http://www.rfc-editor.org/info/rfc4949>. <http://www.rfc-editor.org/info/rfc4949>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>. <http://www.rfc-editor.org/info/rfc5246>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<http://www.rfc-editor.org/info/rfc6690>. <http://www.rfc-editor.org/info/rfc6690>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012, RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>. <http://www.rfc-editor.org/info/rfc6749>.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<http://www.rfc-editor.org/info/rfc6750>.
[RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0 [RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0
Threat Model and Security Considerations", RFC 6819, Threat Model and Security Considerations", RFC 6819,
DOI 10.17487/RFC6819, January 2013, DOI 10.17487/RFC6819, January 2013,
<http://www.rfc-editor.org/info/rfc6819>. <http://www.rfc-editor.org/info/rfc6819>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <http://www.rfc-editor.org/info/rfc7049>. October 2013, <http://www.rfc-editor.org/info/rfc7049>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
skipping to change at page 40, line 5 skipping to change at page 40, line 19
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>. <http://www.rfc-editor.org/info/rfc7231>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<http://www.rfc-editor.org/info/rfc7519>. <http://www.rfc-editor.org/info/rfc7519>.
[RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
RFC 7591, DOI 10.17487/RFC7591, July 2015,
<http://www.rfc-editor.org/info/rfc7591>.
[RFC7744] Seitz, L., Ed., Gerdes, S., Ed., Selander, G., Mani, M.,
and S. Kumar, "Use Cases for Authentication and
Authorization in Constrained Environments", RFC 7744,
DOI 10.17487/RFC7744, January 2016,
<http://www.rfc-editor.org/info/rfc7744>.
Appendix A. Design Justification Appendix A. Design Justification
This section provides further insight into the design decisions of This section provides further insight into the design decisions of
the solution documented in this document. Section 3 lists several the solution documented in this document. Section 3 lists several
building blocks and briefly summarizes their importance. The building blocks and briefly summarizes their importance. The
justification for offering some of those building blocks, as opposed justification for offering some of those building blocks, as opposed
to using OAuth 2.0 as is, is given below. to using OAuth 2.0 as is, is given below.
Common IoT constraints are: Common IoT constraints are:
skipping to change at page 41, line 40 skipping to change at page 42, line 17
The communication interactions this framework builds upon (as The communication interactions this framework builds upon (as
shown graphically in Figure 1) may be accomplished using a variety shown graphically in Figure 1) may be accomplished using a variety
of different protocols, and not all parts of the message flow are of different protocols, and not all parts of the message flow are
used in all applications due to the communication constraints. used in all applications due to the communication constraints.
While we envision deployments to make use of CoAP we explicitly While we envision deployments to make use of CoAP we explicitly
want to support HTTP, HTTP/2 or specific protocols, such as want to support HTTP, HTTP/2 or specific protocols, such as
Bluetooth Smart communication, which does not necessarily use IP. Bluetooth Smart communication, which does not necessarily use IP.
The latter raises the need for application layer security over the The latter raises the need for application layer security over the
various interfaces. various interfaces.
Appendix B. Roles and Responsibilites -- a Checklist Appendix B. Roles and Responsibilites
Resource Owner Resource Owner
* Make sure that the RS is registered at the AS. * Make sure that the RS is registered at the AS.
* Make sure that clients can discover the AS which is in charge * Make sure that clients can discover the AS which is in charge
of the RS. of the RS.
* Make sure that the AS has the necessary, up-to-date, access * Make sure that the AS has the necessary, up-to-date, access
control policies for the RS. control policies for the RS.
Requesting Party Requesting Party
* Make sure that the client is provisioned the necessary * Make sure that the client is provisioned the necessary
credentials to authenticate to the AS. credentials to authenticate to the AS.
* Make sure that the client is configured to follow the security * Make sure that the client is configured to follow the security
requirements of the Requesting Party, when issuing requests requirements of the Requesting Party, when issuing requests
(e.g. minimum communication security requirements, trust (e.g. minimum communication security requirements, trust
anchors). anchors).
* Register the client at the AS. * Register the client at the AS.
Authorization Server Authorization Server
* Register RS and manage corresponding security contexts. * Register RS and manage corresponding security contexts.
* Register clients and including authentication credentials. * Register clients and including authentication credentials.
* Allow Resource Owners to configure and update access control
* Allow Resource Onwers to configure and update access control
policies related to their registered RS' policies related to their registered RS'
* Expose a service that allows clients to request tokens. * Expose a service that allows clients to request tokens.
* Authenticate clients that wishes to request a token. * Authenticate clients that wishes to request a token.
* Process a token requests against the authorization policies * Process a token requests against the authorization policies
configured for the RS. configured for the RS.
* Expose a service that allows RS's to submit token introspection * Expose a service that allows RS's to submit token introspection
requests. requests.
* Authenticate RS's that wishes to get an introspection response. * Authenticate RS's that wishes to get an introspection response.
* Process token introspection requests. * Process token introspection requests.
* Optionally: Handle token revocation. * Optionally: Handle token revocation.
Client Client
* Discover the AS in charge of the RS that is to be targeted with * Discover the AS in charge of the RS that is to be targeted with
a request. a request.
* Submit the token request (A). * Submit the token request (A).
+ Authenticate towards the AS. + Authenticate towards the AS.
+ Specify which RS, which resource(s), and which action(s) the + Specify which RS, which resource(s), and which action(s) the
request(s) will target. request(s) will target.
+ Specify preferences for communication security + Specify preferences for communication security
+ If raw public key (rpk) or certificate is used, make sure + If raw public key (rpk) or certificate is used, make sure
the AS has the right rpk or certificate for this client. the AS has the right rpk or certificate for this client.
* Process the access token and client information (B) * Process the access token and client information (B)
+ Check that the token has the right format (e.g. CWT). + Check that the token has the right format (e.g. CWT).
+ Check that the client information provides the necessary + Check that the client information provides the necessary
security parameters (e.g. PoP key, information on security parameters (e.g. PoP key, information on
communication security protocols supported by the RS). communication security protocols supported by the RS).
* Send the token and request to the RS (C) * Send the token and request to the RS (C)
+ Authenticate towards the RS (this could coincide with the + Authenticate towards the RS (this could coincide with the
proof of possession process). proof of possession process).
+ Transmit the token as specified by the AS (default is to an + Transmit the token as specified by the AS (default is to an
authorization information resource, alternative options are authorization information resource, alternative options are
as a CoAP option or in the DTLS handshake). as a CoAP option or in the DTLS handshake).
+ Perform the proof-of-possession procedure as specified for + Perform the proof-of-possession procedure as specified for
the type of used token (this may already have been taken the type of used token (this may already have been taken
care of through the authentication procedure). care of through the authentication procedure).
* Process the RS response (F) requirements of the Requesting * Process the RS response (F) requirements of the Requesting
Party, when issuing requests (e.g. minimum communication Party, when issuing requests (e.g. minimum communication
security requirements, trust anchors). security requirements, trust anchors).
* Register the client at the AS. * Register the client at the AS.
Resource Server Resource Server
* Expose a way to submit access tokens. * Expose a way to submit access tokens.
* Process an access token. * Process an access token.
+ Verify the token is from the right AS. + Verify the token is from the right AS.
+ Verify that the token applies to this RS. + Verify that the token applies to this RS.
+ Check that the token has not expired (if the token provides + Check that the token has not expired (if the token provides
expiration information). expiration information).
+ Check the token's integrity. + Check the token's integrity.
+ Store the token so that it can be retrieved in the context + Store the token so that it can be retrieved in the context
of a matching request. of a matching request.
* Process a request. * Process a request.
+ Set up communication security with the client. + Set up communication security with the client.
+ Authenticate the client. + Authenticate the client.
+ Match the client against existing tokens. + Match the client against existing tokens.
+ Check that tokens belonging to the client actually authorize + Check that tokens belonging to the client actually authorize
the requested action. the requested action.
+ Optionally: Check that the matching tokens are still valid + Optionally: Check that the matching tokens are still valid
(if this is possible. (if this is possible.
* Send a response following the agreed upon communication * Send a response following the agreed upon communication
security. security.
Appendix C. Optimizations Appendix C. Deployment Examples
This section sketches some potential optimizations to the presented There is a large variety of IoT deployments, as is indicated in
solution. Appendix A, and this section highlights a few common variants. This
section is not normative but illustrates how the framework can be
applied.
Access token in DTLS handshake For each of the deployment variants there are a number of possible
security setups between clients, resource servers and authorization
servers. The main focus in the following subsections is on how
authorization of a client request for a resource hosted by a RS is
performed. This requires the the security of the requests and
responses between the clients and the RS to consider.
In the case of CSP=DTLS/TLS, the access token provisioning Note: CBOR diagnostic notation is used for examples of requests and
exchange in step C of the protocol may be embedded in the security responses.
handshake. Different solutions are possible, where one
standardized method would be the use of the TLS supplemental data
extension [RFC4680] for transferring the access token.
Reference token and introspection C.1. Local Token Validation
In case of introspection it may be beneficial to utilize access In this scenario we consider the case where the resource server is
tokens which are not self-contained (also known as "reference offline, i.e. it is not connected to the AS at the time of the access
tokens") that are used to lookup detailed information about the request. This access procedure involves steps A, B, C, and F of
authorization. The RS uses the introspection message exchange not Figure 1.
only for validating token claims, but also for obtaining claims
that potentially were not known at the time when the access token
was issued.
A reference token can be made much more compact than a self- Since the resource server must be able to verify the access token
contained token, since it does not need to contain any of claims locally, self-contained access tokens must be used.
that it represents. This could be very useful in particular if
the client is constrained and offline most of the time.
Reference token in CoAP option This example shows the interactions between a client, the
authorization server and a temperature sensor acting as a resource
server. Message exchanges A and B are shown in Figure 17.
While large access tokens must be sent in CoAP payload, if the A: The client first generates a public-private key pair used for
access token is known to be of a certain limited size, for example communication security with the RS.
in the case of a reference token, then it would be favorable to The client sends the POST request to /token at the AS. The
combine the access token provisioning request with the resource request contains the public key of the client and the Audience
request to the RS. parameter set to "tempSensorInLivingRoom", a value that the
temperature sensor identifies itself with. The AS evaluates the
request and authorizes the client to access the resource.
One way to achieve this is to define a new CoAP option for B: The AS responds with a PoP token and client information. The
carrying reference tokens, called "Ref-Token" as shown in the PoP token contains the public key of the client, and the client
example in Figure 28. information contains the public key of the RS. For communication
security this example uses DTLS RawPublicKey between the client
and the RS. The issued token will have a short validity time,
i.e. 'exp' close to 'iat', to protect the RS from replay attacks
since it, that cannot do introspection to check the tokens current
validity. The token includes the claim "aif" with the authorized
access that an owner of the temperature device can enjoy. The
'aif' claim, issued by the AS, informs the RS that the owner of
the token, that can prove the possession of a key is authorized to
make a GET request against the /temperature resource and a POST
request on the /firmware resource.
Note: In this example we assume that the client knows what
resource it wants to access, and is therefore able to request
specific audience and scope claims for the access token.
Resource Authorization
Client Server Client Server
| | | |
C: +-------->| Header: PUT (Code=0.02)
| PUT | Ref-Token:SlAV32hkKG
| | Object-Security:
| | <seq>,<cid>,[Uri-Path:"lock", 1],<tag>)
| | | |
. . A: +-------->| Header: POST (Code=0.02)
. . | POST | Uri-Path:"token"
. . | | Content-Type: application/cbor
| | Payload: <Request-Payload>
| | | |
F: |<--------+ Header: 2.04 Changed B: |<--------+ Header: 2.05 Content
| 2.04 | Object-Security: | 2.05 | Content-Type: application/cbor
| | (<seq>,<cid>,,<tag>) | | Payload: <Response-Payload>
| | | |
Figure 28: Reference Token in CoAP Option Figure 17: Token Request and Response Using Client Credentials.
Appendix D. CoAP and CBOR profiles for OAuth 2.0
Many IoT devices can support OAuth 2.0 without any additional
extensions, but for certain constrained settings additional profiling
is needed. In this appendix we define CoAP resources for the HTTP
based token and introspection endpoints used in vanilla OAuth 2.0.
We also define a CBOR alternative to the JSON and form based POST
structures used in HTTP.
D.1. Profile for Token resource
The token resource is used by the client to obtain an access token by
presenting its authorization grant or client credentials to the
/token resource the AS.
D.1.1. Token Request
The client makes a request to the token resource by sending a CBOR
structure with the following attributes.
grant_type:
REQUIRED. The grant type, "code", "client_credentials",
"password" or others.
client_id:
OPTIONAL. The client identifier issued to the holder of the token
(client or RS) during the registration process.
client_secret:
OPTIONAL. The client secret.
scope:
OPTIONAL. The scope of the access request as described by
Section 3.1.
aud:
OPTIONAL. Service-specific string identifier or list of string
identifiers representing the intended audience for this token, as
defined in [I-D.wahlstroem-ace-cbor-web-token].
alg:
OPTIONAL. The value in the 'alg' parameter together with value
from the 'token_type' parameter allow the client to indicate the
supported algorithms for a given token type.
key:
OPTIONAL. This field contains information about the public key
the client would like to bind to the access token in the COSE Key
Structure format.
The parameters defined above use the following CBOR major types.
/-----------+--------------+-----------------------\
| Value | Major Type | Key |
|-----------+--------------+-----------------------|
| 0 | 0 | grant_type |
| 1 | 0 | client_id |
| 2 | 0 | client_secret |
| 3 | 0 | scope |
| 4 | 0 | aud |
| 5 | 0 | alg |
| 6 | 0 | key |
\-----------+--------------+-----------------------/
Figure 29: CBOR mappings used in token requests
D.1.2. Token Response
The AS responds by sending a CBOR structure with the following
attributes.
access_token:
REQUIRED. The access token issued by the authorization server.
token_type:
REQUIRED. The type of the token issued. "pop" is recommended.
key:
REQUIRED, if symmetric key cryptography is used. A COSE Key
Structure containing the symmetric proof of possession key. The
members of the structure can be found in section 7.1 of
[I-D.ietf-cose-msg].
csp:
REQUIRED. Information on what communication protocol to use in
the communication between the client and the RS. Details on
possible values can be found in Section 5.1.
scope:
OPTIONAL, if identical to the scope requested by the client;
otherwise, REQUIRED.
alg:
OPTIONAL. The 'alg' parameter provides further information about
the algorithm, such as whether a symmetric or an asymmetric
crypto-system is used.
The parameters defined above use the following CBOR major types.
/-----------+--------------+-----------------------\
| Value | Major Type | Key |
|-----------+--------------+-----------------------|
| 0 | 0 | access_token |
| 1 | 0 | token_type |
| 2 | 0 | key |
| 3 | 0 | csp |
| 4 | 0 | scope |
| 5 | 0 | alg |
\-----------+--------------+-----------------------/
Figure 30: CBOR mappings used in token responses
D.2. CoAP Profile for OAuth Introspection
This section defines a way for a holder of access tokens, mainly
clients and RS's, to get metadata like validity status, claims and
scopes found in access token. The OAuth Token Introspection
specification [I-D.ietf-oauth-introspection] defines a way to
validate the token using HTTP POST or HTTP GET. This document reuses
the work done in the OAuth Token Introspection and defines a mapping
of the request and response to CoAP [RFC7252] to be used by
constrained devices.
D.2.1. Introspection Request
The token holder makes a request to the Introspection CoAP resource
by sending a CBOR structure with the following attributes.
token:
REQUIRED. The string value of the token.
resource_id:
OPTIONAL. A service-specific string identifying the resource that
the client doing the introspection is asking about.
client_id:
OPTIONAL. The client identifier issued to the holder of the token The information contained in the Request-Payload and the Response-
(client or RS) during the registration process. Payload is shown in Figure 18.
client_secret: Request-Payload :
{
"grant_type" : "client_credentials",
"aud" : "tempSensorInLivingRoom",
"client_id" : "myclient",
"client_secret" : "qwerty"
}
OPTIONAL. The client secret. Response-Payload :
{
"access_token" : b64'SlAV32hkKG ...',
"token_type" : "pop",
"csp" : "DTLS",
"cnf" : {
"COSE_Key" : {
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk',
"kty" : "EC",
"crv" : "P-256",
"x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4',
"y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM'
}
}
}
The parameters defined above use the following CBOR major types: Figure 18: Request and Response Payload Details.
/-----------+--------------+-----------------------\ The content of the access token is shown in Figure 19.
| Value | Major Type | Key |
|-----------+--------------+-----------------------|
| 0 | 0 | token |
| 1 | 0 | resource_id |
| 2 | 0 | client_id |
| 3 | 0 | client_secret |
\-----------+--------------+-----------------------/
Figure 31: CBOR Mappings to Token Introspection Request Parameters. {
"aud" : "tempSensorInLivingRoom",
"iat" : "1360189224",
"exp" : "1360289224",
"aif" : [["/temperature", 0], ["/firmware", 2]],
"cnf" : {
"jwk" : {
"kid" : b64'1Bg8vub9tLe1gHMzV76e8',
"kty" : "EC",
"crv" : "P-256",
"x" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU',
"y" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0'
}
}
}
D.2.2. Introspection Response Figure 19: Access Token including Public Key of the Client.
If the introspection request is valid and authorized, the Messages C and F are shown in Figure 20 - Figure 21.
authorization server returns a CoAP message with the response encoded
as a CBOR structure in the payload of the message. If the request
failed client authentication or is invalid, the authorization server
returns an error response using the CoAP 4.00 'Bad Request' response
code.
The JSON structure in the payload response includes the top-level C: The client then sends the PoP token to the /authz-info resource
members defined in Section 2.2 in the OAuth Token Introspection at the RS. This is a plain CoAP request, i.e. no transport or
specification [I-D.ietf-oauth-introspection]. It is RECOMMENDED to application layer security between client and RS, since the token
only return the 'active' attribute considering constrained nature of is integrity protected between AS and RS. The RS verifies that
CoAP client and server networks. the PoP token was created by a known and trusted AS, is valid, and
responds to the client. The RS caches the security context
together with authorization information about this client
contained in the PoP token.
Introspection responses in CBOR use the following mappings: Resource
Client Server
| |
C: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"authz-info"
| | Payload: SlAV32hkKG ...
| |
|<--------+ Header: 2.01 Created
| 2.01 |
| |
active: Figure 20: Access Token provisioning to RS
The client and the RS runs the DTLS handshake using the raw public
keys established in step B and C.
The client sends the CoAP request GET to /temperature on RS over
DTLS. The RS verifies that the request is authorized, based on
previously established security context.
F: The RS responds with a resource representation over DTLS.
REQUIRED. The active key is an indicator of whether or not the Resource
presented token is currently active. The specifics of a token's Client Server
"active" state will vary depending on the implementation of the | |
authorization server, and the information it keeps about its |<=======>| DTLS Connection Establishment
tokens, but a "true" value return for the "active" property will | | using Raw Public Keys
generally indicate that a given token has been issued by this | |
authorization server, has not been revoked by the resource owner, +-------->| Header: GET (Code=0.01)
and is within its given time window of validity (e.g., after its | GET | Uri-Path: "temperature"
issuance time and before its expiration time). | |
| |
| |
F: |<--------+ Header: 2.05 Content
| 2.05 | Payload: <sensor value>
| |
scope: Figure 21: Resource Request and Response protected by DTLS.
OPTIONAL. A string containing a space-separated list of scopes C.2. Introspection Aided Token Validation
associated with this token, in the format described in Section 3.3
of OAuth 2.0 [RFC6749].
client_id: In this deployment scenario we assume that a client is not be able to
access the AS at the time of the access request. Since the RS is,
however, connected to the back-end infrastructure it can make use of
token introspection. This access procedure involves steps A-F of
Figure 1, but assumes steps A and B have been carried out during a
phase when the client had connectivity to AS.
OPTIONAL. Client identifier for the client that requested this Since the client is assumed to be offline, at least for a certain
token. period of time, a pre-provisioned access token has to be long-lived.
The resource server may use its online connectivity to validate the
access token with the authorization server, which is shown in the
example below.
username: In the example we show the interactions between an offline client
(key fob), a resource server (online lock), and an authorization
server. We assume that there is a provisioning step where the client
has access to the AS. This corresponds to message exchanges A and B
which are shown in Figure 22.
OPTIONAL. Human-readable identifier for the resource owner who Authorization consent from the resource owner can be pre-configured,
authorized this token. but it can also be provided via an interactive flow with the resource
owner. An example of this for the key fob case could be that the
resource owner has a connected car, he buys a generic key that he
wants to use with the car. To authorize the key fob he connects it
to his computer that then provides the UI for the device. After that
OAuth 2.0 implicit flow can used to authorize the key for his car at
the the car manufacturers AS.
token_type: Note: In this example the client does not know the exact door it will
be used to access since the token request is not send at the time of
access. So the scope and audience parameters is set quite wide to
start with and new values different form the original once can be
returned from introspection later on.
OPTIONAL. Type of the token as defined in Section 5.1 of OAuth A: The client sends the request using POST to /token at AS. The
2.0 [RFC6749] or PoP token. request contains the Audience parameter set to "PACS1337" (PACS,
Physical Access System), a value the that the online door in
question identifies itself with. The AS generates an access token
as on opaque string, which it can match to the specific client, a
targeted audience and a symmetric key.
B: The AS responds with the an access token and client
information, the latter containing a symmetric key. Communication
security between C and RS will be DTLS and PreSharedKey. The PoP
key being used as the PreSharedKey.
exp: Authorization
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"token"
| | Content-Type: application/cbor
| | Payload: <Request-Payload>
| |
B: |<--------+ Header: 2.05 Content
| | Content-Type: application/cbor
| 2.05 | Payload: <Response-Payload>
| |
OPTIONAL. Integer timestamp, measured in the number of seconds Figure 22: Token Request and Response using Client Credentials.
since January 1 1970 UTC, indicating when this token will expire,
as defined in CWT [I-D.wahlstroem-ace-cbor-web-token].
iat: The information contained in the Request-Payload and the Response-
Payload is shown in Figure 23.
OPTIONAL. Integer timestamp, measured in the number of seconds Request-Payload:
since January 1 1970 UTC, indicating when this token will expire, {
as defined in CWT [I-D.wahlstroem-ace-cbor-web-token]. "grant_type" : "client_credentials",
"aud" : "lockOfDoor4711",
"client_id" : "keyfob",
"client_secret" : "qwerty"
}
nbf: Response-Payload:
{
"access_token" : b64'SlAV32hkKG ...'
"token_type" : "pop",
"csp" : "DTLS",
"cnf" : {
"COSE_Key" : {
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk',
"kty" : "oct",
"alg" : "HS256",
"k": b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE'
}
}
}
OPTIONAL. Integer timestamp, measured in the number of seconds Figure 23: Request and Response Payload for C offline
since January 1 1970 UTC, indicating when this token will expire,
as defined in CWT [I-D.wahlstroem-ace-cbor-web-token].
sub: The access token in this case is just an opaque string referencing
the authorization information at the AS.
OPTIONAL. Subject of the token, as defined in CWT C: Next, the client POSTs the access token to the /authz-info
[I-D.wahlstroem-ace-cbor-web-token]. Usually a machine-readable resource in the RS. This is a plain CoAP request, i.e. no DTLS
identifier of the resource owner who authorized this token. between client and RS. Since the token is an opaque string, the
RS cannot verify it on its own, and thus defers to respond the
client with a status code until after step E.
D: The RS forwards the token to the /introspect resource on the
AS. Introspection assumes a secure connection between the AS and
the RS, e.g. using transport of application layer security, which
is not detailed in this example.
E: The AS provides the introspection response containing
parameters about the token. This includes the confirmation key
(cnf) parameter that allows the RS to verify the client's proof of
possession in step F.
After receiving message E, the RS responds to the client's POST in
step C with Code 2.01 Created.
aud: Resource
Client Server
| |
C: +-------->| Header: POST (T=CON, Code=0.02)
| POST | Uri-Path:"authz-info"
| | Content-Type: "application/cbor"
| | Payload: b64'SlAV32hkKG ...''
| |
| | Authorization
| | Server
| | |
D: | +--------->| Header: POST (Code=0.02)
| | POST | Uri-Path: "introspect"
| | | Content-Type: "application/cbor"
| | | Payload: <Request-Payload>
| | |
E: | |<---------+ Header: 2.05 Content
| | 2.05 | Content-Type: "application/cbor"
| | | Payload: <Response-Payload>
| | |
| |
C: |<--------+ Header: 2.01 Created
| 2.01 |
| |
OPTIONAL. Service-specific string identifier or list of string Figure 24: Token Introspection for C offline
identifiers representing the intended audience for this token, as The information contained in the Request-Payload and the Response-
defined in CWT [I-D.wahlstroem-ace-cbor-web-token]. Payload is shown in Figure 25.
iss: Request-Payload:
{
"token" : b64'SlAV32hkKG...',
"client_id" : "FrontDoor",
"client_secret" : "ytrewq"
}
OPTIONAL. String representing the issuer of this token, as Response-Payload:
defined in CWT [I-D.wahlstroem-ace-cbor-web-token]. {
"active" : true,
"aud" : "lockOfDoor4711",
"scope" : "open, close",
"iat" : 1311280970,
"cnf" : {
"kid" : b64'JDLUhTMjU2IiwiY3R5Ijoi ...'
}
}
cti: Figure 25: Request and Response Payload for Introspection
OPTIONAL. String identifier for the token, as defined in CWT The client uses the symmetric PoP key to establish a DTLS
[I-D.wahlstroem-ace-cbor-web-token] PreSharedKey secure connection to the RS. The CoAP request PUT is
sent to the uri-path /state on RS changing state of the door to
locked.
F: The RS responds with a appropriate over the secure DTLS
channel.
The parameters defined above use the following CBOR major types: Resource
Client Server
| |
|<=======>| DTLS Connection Establishment
| | using Pre Shared Key
| |
+-------->| Header: PUT (Code=0.03)
| PUT | Uri-Path: "state"
| | Payload: <new state for the lock>
| |
F: |<--------+ Header: 2.04 Changed
| 2.04 | Payload: <new state for the lock>
| |
/-----------+--------------+-----------------------\ Figure 26: Resource request and response protected by OSCOAP
| Value | Major Type | Key |
|-----------+--------------+-----------------------|
| 0 | 0 | active |
| 1 | 0 | scopes |
| 2 | 0 | client_id |
| 3 | 0 | username |
| 4 | 0 | token_type |
| 5 | 0 | exp |
| 6 | 0 | iat |
| 7 | 0 | nbf |
| 8 | 0 | sub |
| 9 | 0 | aud |
| 10 | 0 | iss |
| 11 | 0 | cti |
\-----------+--------------+-----------------------/
Figure 32: CBOR Mappings to Token Introspection Response Parameters. Appendix D. Document Updates
D.1. Version -01 to -02
Appendix E. Document Updates o Restructured to remove communication security parts. These shall
now be defined in profiles.
o Restructured section 5 to create new sections on the OAuth
endpoints /token, /introspect and /authz-info.
o Pulled in material from draft-ietf-oauth-pop-key-distribution in
order to define proof-of-possession key distribution.
o Introduced the 'cnf' parameter as defined in RFC7800 to reference
or transport keys used for proof of posession.
o Introduced the 'client-token' to transport client information from
the AS to the client via the RS in conjunction with introspection.
o Expanded the IANA section to define parameters for token request,
introspection and CWT claims.
o Moved deployment scenarios to the appendix as examples.
E.1. Version -00 to -01 D.2. Version -00 to -01
o Changed 5.1. from "Communication Security Protocol" to "Client o Changed 5.1. from "Communication Security Protocol" to "Client
Information". Information".
o Major rewrite of 5.1 to clarify the information exchanged between o Major rewrite of 5.1 to clarify the information exchanged between
C and AS in the PoP token request profile for IoT. C and AS in the PoP token request profile for IoT.
* Allow the client to indicate preferences for the communication * Allow the client to indicate preferences for the communication
security protocol. security protocol.
* Defined the term "Client Information" for the additional * Defined the term "Client Information" for the additional
information returned to the client in addition to the access information returned to the client in addition to the access
token. token.
* Require that the messages between AS and client are secured, * Require that the messages between AS and client are secured,
either with (D)TLS or with COSE_Encrypted wrappers. either with (D)TLS or with COSE_Encrypted wrappers.
* Removed dependency on OSCoAP and added generic text about * Removed dependency on OSCoAP and added generic text about
object security instead. object security instead.
* Defined the "rpk" parameter in the client information to * Defined the "rpk" parameter in the client information to
transmit the raw public key of the RS from AS to client. transmit the raw public key of the RS from AS to client.
* (D)TLS MUST use the PoP key in the handshake (either as PSK or * (D)TLS MUST use the PoP key in the handshake (either as PSK or
as client RPK with client authentication). as client RPK with client authentication).
* Defined the use of x5c, x5t and x5tS256 parameters when a * Defined the use of x5c, x5t and x5tS256 parameters when a
client certificate is used for proof of possession. client certificate is used for proof of possession.
* Defined "tktn" parameter for signaling for how to transfer the
* Defined "tktn" parameter for signaling for how to tranfer the
access token. access token.
o Added 5.2. the CoAP Access-Token option for transferring access
o Added 5.2. the CoAP Access-Token option for transfering access
tokens in messages that do not have payload. tokens in messages that do not have payload.
o 5.3.2. Defined success and error responses from the RS when o 5.3.2. Defined success and error responses from the RS when
receiving an access token. receiving an access token.
o 5.6.:Added section giving guidance on how to handle token o 5.6.:Added section giving guidance on how to handle token
expiration in the absence of reliable time. expiration in the absence of reliable time.
o Appendix B Added list of roles and responsibilities for C, AS and o Appendix B Added list of roles and responsibilities for C, AS and
RS. RS.
Authors' Addresses Authors' Addresses
Ludwig Seitz Ludwig Seitz
SICS SICS
Scheelevaegen 17 Scheelevaegen 17
Lund 223 70 Lund 223 70
SWEDEN SWEDEN
skipping to change at page 53, line 4 skipping to change at page 53, line 22
Email: ludwig@sics.se Email: ludwig@sics.se
Goeran Selander Goeran Selander
Ericsson Ericsson
Faroegatan 6 Faroegatan 6
Kista 164 80 Kista 164 80
SWEDEN SWEDEN
Email: goran.selander@ericsson.com Email: goran.selander@ericsson.com
Erik Wahlstroem Erik Wahlstroem
Nexus Technology Nexus Technology
Telefonvagen 26 Telefonvagen 26
Hagersten 126 26 Hagersten 126 26
Sweden Sweden
Email: erik.wahlstrom@nexusgroup.com Email: erik.wahlstrom@nexusgroup.com
Samuel Erdtman Samuel Erdtman
Nexus Technology Spotify AB
Telefonvagen 26 Birger Jarlsgatan 61, 4tr
Hagersten 126 26 Stockholm 113 56
Sweden Sweden
Email: samuel.erdtman@nexusgroup.com Email: erdtman@spotify.com
Hannes Tschofenig Hannes Tschofenig
ARM Ltd. ARM Ltd.
Hall in Tirol 6060 Hall in Tirol 6060
Austria Austria
Email: Hannes.Tschofenig@arm.com Email: Hannes.Tschofenig@arm.com
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