--- 1/draft-ietf-ace-oauth-authz-02.txt 2016-10-12 05:16:21.227649504 -0700 +++ 2/draft-ietf-ace-oauth-authz-03.txt 2016-10-12 05:16:21.335652135 -0700 @@ -1,52 +1,52 @@ ACE Working Group L. Seitz Internet-Draft SICS Intended status: Standards Track G. Selander -Expires: December 12, 2016 Ericsson +Expires: April 15, 2017 Ericsson E. Wahlstroem - Nexus Technology + S. Erdtman Spotify AB H. Tschofenig ARM Ltd. - June 10, 2016 + October 12, 2016 Authentication and Authorization for Constrained Environments (ACE) - draft-ietf-ace-oauth-authz-02 + draft-ietf-ace-oauth-authz-03 Abstract - This specification defines the ACE framework for authentication and - authorization in Internet of Things (IoT) deployments. The ACE + This specification defines a framework for authentication and + authorization in Internet of Things (IoT) environments. The framework is based on a set of building blocks including OAuth 2.0 and CoAP, thus making a well-known and widely used authorization 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. + where possible, but where the constraints of IoT devices require it, + extensions are added and profiles are defined. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on December 12, 2016. + This Internet-Draft will expire on April 15, 2017. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -58,98 +58,93 @@ Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. OAuth 2.0 . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2. CoAP . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 9 5. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 13 - 6. The 'Token' Resource . . . . . . . . . . . . . . . . . . . . 14 + 6. The 'Token' Endpoint . . . . . . . . . . . . . . . . . . . . 14 6.1. Client-to-AS Request . . . . . . . . . . . . . . . . . . 14 6.2. AS-to-Client Response . . . . . . . . . . . . . . . . . . 17 6.3. Error Response . . . . . . . . . . . . . . . . . . . . . 18 6.4. New Request and Response Parameters . . . . . . . . . . . 18 - 6.4.1. Grant Type . . . . . . . . . . . . . . . . . . . . . 19 - 6.4.2. Token Type and Algorithms . . . . . . . . . . . . . . 19 - 6.4.3. Profile . . . . . . . . . . . . . . . . . . . . . . . 20 - 6.4.4. Confirmation . . . . . . . . . . . . . . . . . . . . 20 - 6.5. Mapping parameters to CBOR . . . . . . . . . . . . . . . 22 - 7. The 'Introspect' Resource . . . . . . . . . . . . . . . . . . 22 + 6.4.1. Audience . . . . . . . . . . . . . . . . . . . . . . 18 + 6.4.2. Grant Type . . . . . . . . . . . . . . . . . . . . . 19 + 6.4.3. Token Type . . . . . . . . . . . . . . . . . . . . . 19 + 6.4.4. Profile . . . . . . . . . . . . . . . . . . . . . . . 19 + 6.4.5. Confirmation . . . . . . . . . . . . . . . . . . . . 20 + 6.5. Mapping parameters to CBOR . . . . . . . . . . . . . . . 21 + 7. The 'Introspect' Endpoint . . . . . . . . . . . . . . . . . . 22 7.1. RS-to-AS Request . . . . . . . . . . . . . . . . . . . . 23 7.2. AS-to-RS Response . . . . . . . . . . . . . . . . . . . . 23 7.3. Error Response . . . . . . . . . . . . . . . . . . . . . 24 7.4. Client Token . . . . . . . . . . . . . . . . . . . . . . 25 7.5. Mapping Introspection parameters to CBOR . . . . . . . . 26 8. The Access Token . . . . . . . . . . . . . . . . . . . . . . 27 - 8.1. The 'Authorization Information' Resource . . . . . . . . 27 + 8.1. The 'Authorization Information' Endpoint . . . . . . . . 28 8.2. Token Expiration . . . . . . . . . . . . . . . . . . . . 28 - 9. Security Considerations . . . . . . . . . . . . . . . . . . . 28 - 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 - 10.1. OAuth Introspection Response Parameter Registration . . 29 - 10.2. OAuth Parameter Registration . . . . . . . . . . . . . . 30 - 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 B. Roles and Responsibilites . . . . . . . . . . . . . 42 - Appendix C. Deployment Examples . . . . . . . . . . . . . . . . 44 - C.1. Local Token Validation . . . . . . . . . . . . . . . . . 44 - C.2. Introspection Aided Token Validation . . . . . . . . . . 48 - Appendix D. Document Updates . . . . . . . . . . . . . . . . . . 51 - D.1. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 52 - D.2. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 52 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53 + 9. Security Considerations . . . . . . . . . . . . . . . . . . . 29 + 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 + 10.1. OAuth Introspection Response Parameter Registration . . 30 + 10.2. OAuth Parameter Registration . . . . . . . . . . . . . . 31 + 10.3. OAuth Access Token Types . . . . . . . . . . . . . . . . 31 + 10.4. Token Type Mappings . . . . . . . . . . . . . . . . . . 32 + 10.4.1. Registration Template . . . . . . . . . . . . . . . 32 + 10.4.2. Initial Registry Contents . . . . . . . . . . . . . 32 + 10.5. CBOR Web Token Claims . . . . . . . . . . . . . . . . . 32 + 10.6. ACE Profile Registry . . . . . . . . . . . . . . . . . . 33 + 10.6.1. Registration Template . . . . . . . . . . . . . . . 33 + 10.7. OAuth Parameter Mappings Registry . . . . . . . . . . . 33 + 10.7.1. Registration Template . . . . . . . . . . . . . . . 33 + 10.7.2. Initial Registry Contents . . . . . . . . . . . . . 34 + 10.8. Introspection Endpoint CBOR Mappings Registry . . . . . 36 + 10.8.1. Registration Template . . . . . . . . . . . . . . . 36 + 10.8.2. Initial Registry Contents . . . . . . . . . . . . . 36 + 10.9. CoAP Option Number Registration . . . . . . . . . . . . 38 + 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39 + 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 39 + 12.1. Normative References . . . . . . . . . . . . . . . . . . 39 + 12.2. Informative References . . . . . . . . . . . . . . . . . 40 + Appendix A. Design Justification . . . . . . . . . . . . . . . . 42 + Appendix B. Roles and Responsibilites . . . . . . . . . . . . . 44 + Appendix C. Requirements on Profiles . . . . . . . . . . . . . . 46 + Appendix D. Deployment Examples . . . . . . . . . . . . . . . . 46 + D.1. Local Token Validation . . . . . . . . . . . . . . . . . 47 + D.2. Introspection Aided Token Validation . . . . . . . . . . 50 + Appendix E. Document Updates . . . . . . . . . . . . . . . . . . 54 + E.1. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 54 + E.2. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 54 + E.3. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 55 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56 1. Introduction Authorization is the process for granting approval to an entity to access a resource [RFC4949]. The authorization task itself can best be described as granting access to a requesting client, for a 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. - We envision that end consumers and enterprises will manage access to - resources on, or produced by, Internet of Things (IoT) devices in the - same style as they do today with data, services and applications on - the Web or with their mobile devices. This desire will increase with - the number of exposed services and capabilities provided by - applications hosted on the IoT devices. - While prior work on authorization solutions for the Web and for the mobile environment also applies to the IoT environment many IoT devices are constrained, for example in terms of processing capabilities, available memory, etc. For web applications on constrained nodes this specification makes use of CoAP [RFC7252]. A detailed treatment of constraints can be found 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 mains- powered devices, and all levels in between. 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 @@ -189,53 +184,54 @@ 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 authorization server (CAS) functionality is not stand-alone but subsumed by either the authorization server or the client (see section 2.2 in [I-D.ietf-ace-actors]). 3. Overview - This specification describes the ACE framework for authorization in - the Internet of Things consisting of a set of building blocks. + This specification defines the ACE framework for authorization in the + Internet of Things environment. It consists of a set of building + blocks. The basic block is the OAuth 2.0 [RFC6749] framework, which enjoys widespread deployment. Many IoT devices can support OAuth 2.0 without any additional extensions, but for certain constrained settings additional profiling is needed. Another building block is the lightweight web transfer protocol CoAP [RFC7252] for those communication environments where HTTP is not appropriate. CoAP typically runs on top of UDP which further reduces overhead and message exchanges. While this specification defines 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. + underlying protocols to be supported in the future, such as HTTP/2, + MQTT and QUIC. A third building block is CBOR [RFC7049] for encodings where JSON [RFC7159] is not sufficiently compact. CBOR is a binary encoding designed for small code and message size, which may be used for encoding of self contained tokens, and also for encoding CoAP POST parameters and CoAP responses. A fourth building block is the compact CBOR-based secure message format COSE [I-D.ietf-cose-msg], which enables application layer security as an alternative or complement to transport layer security (DTLS [RFC6347] or TLS [RFC5246]). COSE is used to secure self - contained tokens such as proof-of-possession (PoP) tokens - [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]. + contained tokens such as proof-of-possession (PoP) tokens, 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 IoT device and network constraints are possible. A list of constraints is described in detail in RFC 7228 [RFC7228] and a description of how the building blocks mentioned above relate to the various constraints can be found in Appendix A. Luckily, not every IoT device suffers from all constraints. The ACE framework nevertheless takes all these aspects into account and allows several different deployment variants to co-exist rather than @@ -283,85 +279,84 @@ client. Access tokens can have different formats, and various methods of utilization (e.g., cryptographic properties) based on the security requirements of the given deployment. Proof of Possession Tokens: 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 - are called proof-of-possession tokens (or PoP tokens) - [I-D.ietf-oauth-pop-architecture]. + are called proof-of-possession tokens (or PoP tokens). The proof-of-possession (PoP) security concept assumes that the AS acts as a trusted third party that binds keys to access tokens. These so called PoP keys are then used by the client to demonstrate the possession of the secret to the RS when accessing 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 bound to the access token. When this specification uses the term "access 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 symmetric as well as on asymmetric cryptography. The appropriate choice of security depends on the constraints of the IoT devices as well as on the security requirements of the use case. - Symmetric PoP key: The AS generates a random symmetric PoP key, - encrypts it for the RS and includes it inside an access token. - The PoP key is also encrypted for the client and sent together - with the access token to the client.> + Symmetric PoP key: The AS generates a random symmetric PoP key. + The key is either stored to be returned on introspection calls + or encrypted and included in the access token. The PoP key is + 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 public key is sent to the AS (if it does not already have knowledge of the client's public key). Information about the public key, which is the PoP key in this - case, is then included inside the access token and sent back to - the requesting client. The RS can identify the client's public - key from the information in the token, which allows the client - to use the corresponding private key for the proof of - possession. + case, is either stored to be returned on introspection calls or + included inside the access token and sent back to the + requesting client. The RS can identify the client's public key + from the information in the token, which allows the client to + use the corresponding private key for the proof of possession. The access token is protected against modifications using a MAC or a digital signature, which is added by the AS. The choice of PoP key does not necessarily imply a specific credential type for the - integrity protection of the token. More information about PoP - tokens can be found in [I-D.ietf-oauth-pop-architecture]. + integrity protection of the token. Scopes and Permissions: In OAuth 2.0, the client specifies the type of permissions it is - seeking to obtain (via the scope parameter) in the access request. - In turn, the AS may use the scope response parameter to inform the - client of the scope of the access token issued. As the client - could be a constrained device as well, this specification uses - CBOR encoded messages for CoAP, defined in Section 5, to request - scopes and to be informed what scopes the access token was + seeking to obtain (via the scope parameter) in the access token + request. In turn, the AS may use the scope response parameter to + inform the client of the scope of the access token issued. As the + client could be a constrained device as well, this specification + uses CBOR encoded messages for CoAP, defined in Section 5, to + request scopes and to be informed what scopes the access token was actually authorized for by the AS. The values of the scope parameter are expressed as a list of space- delimited, case-sensitive strings, with a semantic that is well-known to the AS and the RS. More details about the concept of scopes is found under Section 3.3 in [RFC6749]. Claims: - Information carried in the access token, called claims, is in the - form of type-value pairs. An access token may, for example, - include a claim identifying the AS that issued the token (via the - "iss" claim) and what audience the access token is intended for - (via the "aud" claim). The audience of an access token can be a - specific resource or one or many resource servers. The resource - owner policies influence what claims are put into the access token - by the authorization server. + Information carried in the access token or returned from + introspection, called claims, is in the form of type-value pairs. + An access token may, for example, include a claim identifying the + AS that issued the token (via the "iss" claim) and what audience + the access token is intended for (via the "aud" claim). The + audience of an access token can be a specific resource or one or + many resource servers. The resource owner policies influence what + claims are put into the access token by the authorization server. While the structure and encoding of the access token varies throughout deployments, a standardized format has been defined with the JSON Web Token (JWT) [RFC7519] where claims are encoded as a JSON object. In [I-D.ietf-ace-cbor-web-token] an equivalent format using CBOR encoding (CWT) has been defined. Introspection: Introspection is a method for a resource server to query the @@ -378,57 +373,78 @@ specifically designed for constrained environments. CoAP typically uses datagram-oriented transport, such as UDP, where reordering and loss of packets can occur. A security solution need to take the latter aspects into account. While HTTP uses headers and query-strings to convey additional information about a request, CoAP encodes such information in so- called 'options'. CoAP supports application-layer fragmentation of the CoAP payloads - through blockwise transfers [I-D.ietf-core-block]. However, block- - wise transfer does not increase the size limits of CoAP options, - therefore data encoded in options has to be kept small. + through blockwise transfers [RFC7959]. However, block-wise transfer + does not increase the size limits of CoAP options, therefore data + encoded in options has to be kept small. Transport layer security for CoAP can be provided by DTLS 1.2 [RFC6347] or TLS 1.2 [RFC5246]. CoAP defines a number of proxy operations which requires transport layer security to be terminated at the proxy. One approach for protecting CoAP communication end-to- end through proxies, and also to support security for CoAP over different transport in a uniform way, is to provide security on application layer using an object-based security mechanism such as - CBOR Encoded Message Syntax [I-D.ietf-cose-msg]. + COSE [I-D.ietf-cose-msg]. One application of COSE is OSCOAP [I-D.selander-ace-object-security], which provides end-to-end confidentiality, integrity and replay protection, and a secure binding between CoAP request and response messages. In OSCOAP, the CoAP messages are wrapped in COSE objects and sent using CoAP. 4. Protocol Interactions The ACE framework is based on the OAuth 2.0 protocol interactions using the /token and /introspect endpoints. A client obtains an access token from an AS using the /token endpoint and subsequently presents the access token to a RS to gain access to a protected 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 OAuth 2.0 framework defines a number of "protocol flows" via + grant types, which have been extended further with extensions to + OAuth 2.0 (such as RFC 7521 [RFC7521] and + [I-D.ietf-oauth-device-flow]). What grant types works best depends + on the usage scenario and RFC 7744 [RFC7744] describes many different + IoT use cases but there two preferred grant types, namely the + Authorization Code Grant (described in Section 4.1 of RFC 7521) and + the Client Credentials Grant (described in Section 4.4 of RFC 7521). + The Authorization Code Grant is a good fit for use with apps running + on smart phones and tablets that request access to IoT devices, a + common scenario in the smart home environment, where users need to go + through an authentication and authorization phase (at least during + the initial setup phase). The native apps guidelines described in + [I-D.ietf-oauth-native-apps] are applicable to this use case. The + Client Credential Grant is a good fit for use with IoT devices where + the OAuth client itself is constraint. In such a case the resource + owner or another person on his or her behalf have arranged with the + authorization server out-of-band, which is often accomplished using + an commissioning tool. + The consent of the resource owner, for giving a client access to a - protected resource, can be pre-configured authorization policies or - dynamically at the time when the request is sent. The resource owner - and the requesting party (i.e. client owner) are not shown in - Figure 1. + protected resource, can be provided dynamically as in the traditional + OAuth flows, or it could be pre-configured by the resource owner as + authorization policies at the AS, which the AS evaluates when a token + request arrives. The resource owner and the requesting party (i.e. + client owner) are not shown in Figure 1. This framework supports a wide variety of communication security mechanisms between the ACE entities, such as client, AS, and RS. We assume that the client has been registered (also called enrolled or onboarded) to an AS using a mechanism defined outside the scope of this document. In practice, various techniques for onboarding have 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 @@ -449,30 +465,29 @@ At the start of the protocol there is an optional discovery step where the client discovers the resource server and the resources this server hosts. In this step the client might also determine what permissions are needed to access the protected resource. The detailed procedures for this discovery process may be defined in an ACE profile and depend on the protocols being used and the specific deployment environment. In Bluetooth Low Energy, for example, advertisements are broadcasted by a peripheral, including information about the primary 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 CoAP, as a second example, a client can make a request to "/.well- + known/core" to obtain information about available resources, which + are returned in a standardized format as described in [RFC6690]. +--------+ +---------------+ | |---(A)-- Token Request ------->| | | | | Authorization | | |<--(B)-- Access Token ---------| Server | - | | + Client Information | | + | | + RS Information | | | | +---------------+ | | ^ | | | Introspection Request (D)| | | Client | | | | | Response + Client Token | |(E) | | | v | | +--------------+ | |---(C)-- Token + Request ----->| | | | | Resource | | |<--(F)-- Protected Resource ---| Server | @@ -488,53 +503,53 @@ Section 3.1 for a short description) wherein the AS binds a key to an access token. The client may include permissions it seeks to obtain, and information about the credentials it wants to use (e.g., symmetric/asymmetric cryptography or a reference to a specific credential). Access Token Response (B): If the AS successfully processes the request from the client, it returns an access token. It also returns various parameters, - referred as "Client Information". In addition to the response + referred as "RS Information". In addition to the response parameters defined by OAuth 2.0 and the PoP token extension, further response parameters, such as information on which profile the client should use with the resource server(s). More information about these parameters can be found in in Section 6.4. Resource Request (C): The client interacts with the RS to request access to the protected resource and provides the access token. The protocol to use between the client and the RS is not restricted to CoAP. HTTP, HTTP/2, QUIC, MQTT, Bluetooth Low Energy, etc., are also viable candidates. Depending on the device limitations and the selected protocol this exchange may be split up into two parts: (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 - communication security protocol and other client information + communication security protocol and other RS Information obtained from the AS. The Client and the RS mutually authenticate using the security protocol specified in the profile (see step B) and the keys - obtained in the access token or the client information or the - client token. The RS verifies that the token is integrity - protected by the AS and compares the claims contained in the - 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. + obtained in the access token or the RS Information or the client + token. The RS verifies that the token is integrity protected by + the AS and compares the claims contained in the 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): A resource server may be configured to introspect the access token by including it in a request to the /introspect endpoint at that AS. Token introspection over CoAP is defined in Section 7 and for HTTP in [RFC7662]. Note that token introspection is an optional step and can be omitted if the token is self-contained and the resource server is @@ -568,538 +583,553 @@ For IoT we cannot generally assume that the client and RS are part of a common key infrastructure, so the AS provisions credentials or associated information to allow mutual authentication. These credentials need to be provided to the parties before or during the authentication protocol is executed, and may be re-used for subsequent token requests. Proof-of-Possession The ACE framework by default implements proof-of-possession for - access tokens, i.e. that the authenticated token holder is bound - to the token. The binding is provided by the "cnf" claim - indicating what key is used for mutual authentication. If clients - need to update a token, e.g. to get additional rights, they can - request that the AS binds the new access token to the same - credential as the previous token. + access tokens, i.e. that the token holder can prove being a holder + of the key bound to the token. The binding is provided by the + "cnf" claim indicating what key is used for mutual authentication. + If clients need to update a token, e.g. to get additional rights, + they can request that the AS binds the new access token to the + same credential as the previous token. - ACE Profile Negotiation + ACE Profiles The client or RS may be limited in the encodings or protocols it supports. To support a variety of different deployment settings, specific interactions between client and RS are defined in an ACE - profile. The ACE framework supports the negotiation of different - ACE profiles between client and AS using the "profile" parameter - in the token request and token response. + profile. In ACE framework the AS is expected to manage the + matching of compatible profile choices between a client and an RS. + The AS informs the client of the selected profile using the + "profile" parameter in the token request and token response. OAuth 2.0 requires the use of TLS both to protect the communication - between AS and client when requesting an access token and between AS - and RS for introspection. In constrained settings TLS is not always - 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. + between AS and client when requesting an access token; between client + and RS when accessing a resource and between AS and RS for + introspection. In constrained settings TLS is not always 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. Profiles are expected to specify the details of how this is done, depending e.g. on the communication protocol and the credentials used by the client or the RS. In OAuth 2.0 the communication with the Token and the Introspection - resources at the AS is assumed to be via HTTP and may use Uri-query + endpoints at the AS is assumed to be via HTTP and may use Uri-query parameters. This framework RECOMMENDS to use CoAP instead and RECOMMENDS the use of the following alternative instead of Uri-query 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. + request. The Content-format depends on the security applied to the + content and must be specified by the corresponding profile. The OAuth 2.0 AS uses a JSON structure in the payload of its responses both to client and RS. This framework RECOMMENDS the use of CBOR [RFC7049] instead. The requesting device can explicitly request this encoding by setting the CoAP Accept option in the - request to "application/cbor". + request to "application/cbor". Depending on the profile, the content + may arrive in a different format wrapping a CBOR payload. -6. The 'Token' Resource +6. The 'Token' Endpoint - In plain OAuth 2.0 the AS provides the /token resource for submitting + In plain OAuth 2.0 the AS provides the /token endpoint for submitting access token requests. This framework extends the functionality of - the /token resource, giving the AS the possibility to help client and + the /token endpoint, giving the AS the possibility to help client and RS to establish shared keys or to exchange their public keys. + Furthermore this framework defines encodings using CoAP and CBOR, + instead of HTTP and JSON. - Communication between the client and the token resource at the AS + Communication between the client and the /token endpoint at the AS MUST be integrity protected and encrypted. Furthermore AS and client MUST perform mutual authentication. 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. 6.1. Client-to-AS Request - When requesting an access token from the AS, the client MAY include - the following parameters in the request in addition to the ones - required or optional according to the OAuth 2.0 specification - [RFC6749]: - - token_type - OPTIONAL. See Section 6.4 for more details. + The client sends a CoAP POST request to the token endpoint at the AS, + the profile is expected to specify the Content-Type and wrapping of + the payload. The content of the request consists of the parameters + specified in section 4 of the OAuth 2.0 specification [RFC6749] + encoded as a CBOR map. - alg - OPTIONAL. See Section 6.4 for more details. + In addition to these parameters, this framework defines the following + parameters for requesting an access token from a /token endpoint: - profile - OPTIONAL. This indicates the profile that the client would like - to use with the RS. See Section 6.4 for more details on the - formatting of this parameter. If the RS cannot support the - requested profile, the AS MUST reply with an error message. + aud + OPTIONAL. Specifies the audience for which the client is + requesting an access token. If this parameter is missing it is + assumed that the client and the AS have a pre-established + understanding of the audience that an access token should address. + If a client submits a request for an access token without + specifying an "aud" parameter, and the AS does not have a default + "aud" value for this client, then the AS MUST respond with an + error message with the CoAP response code 4.00 (Bad Request). cnf - OPTIONAL. This field contains information about a public key the - client would like to bind to the access token. If the client - requests an asymmetric proof-of-possession algorithm, but does not - provide a public key, the AS MUST respond with an error message. - See Section 6.4 for more details on the formatting of the 'cnf' + OPTIONAL. This field contains information about the key the + client would like to bind to the access token for proof-of- + possession. It is NOT RECOMMENDED that a client submits a + symmetric key value to the AS using this parameter. See + Section 6.4.5 for more details on the formatting of the 'cnf' parameter. - These new parameters are optional in the case where the AS has prior - knowledge of the capabilities of the client, otherwise these - parameters are required. This prior knowledge may, for example, be - set by the use of a dynamic client registration protocol exchange - [RFC7591]. - The following examples illustrate different types of requests for proof-of-possession tokens. Figure 2 shows a request for a token with a symmetric proof-of- - possession key. + possession key. Note that in this example we assume a DTLS-based + communication security profile, therefore the Content-Type is + "application/cbor". Header: POST (Code=0.02) 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 key. Figure 3 shows a request for a token with an asymmetric proof-of- - possession key. + possession key. Note that in this example we assume an object + security-based profile, therefore the Content-Type is "application/ + cose+cbor". Header: POST (Code=0.02) Uri-Host: "server.example.com" Uri-Path: "token" - Content-Type: "application/cbor" + Content-Type: "application/cose+cbor" Payload: { - "grant_type" : "token", - "aud" : "lockOfDoor0815", - "client_id" : "myclient", - "token_type" : "pop", - "alg" : "ES256", - "profile" : "coap_oscoap" + "grant_type" : "client_credentials", "cnf" : { "COSE_Key" : { "kty" : "EC", "kid" : h'11', "crv" : "P-256", "x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8', "y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4' } } } Figure 3: Example request for an access token bound to an asymmetric key. Figure 4 shows a request for a token where a previously communicated - proof-of-possession key is only referenced. + proof-of-possession key is only referenced. Note that we assume a + DTLS-based communication security profile for this example, therefore + the Content-Type is "application/cbor". Also note that the client + performs a password based authentication in this example by + submitting its client_secret. Header: POST (Code=0.02) Uri-Host: "server.example.com" Uri-Path: "token" Content-Type: "application/cbor" Payload: { "grant_type" : "client_credentials", + "client_id" : "myclient", + "client_secret" : "mysecret234", "aud" : "valve424", "scope" : "read", - "client_id" : "myclient", - "token_type" : "pop", - "alg" : "ES256", - "profile" : "coap_oscoap" "cnf" : { "kid" : b64'6kg0dXJM13U' } } Figure 4: Example request for an access token bound to a key reference. 6.2. AS-to-Client Response 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. + and the client is authorized to obtain an access token corresponding + to its access token request, the AS sends a response with the CoAP + response code 2.01 (Created). If client request was invalid, or not + authorized, the AS returns an error response as described in + Section 6.3. - The following parameters may also be part of a successful response in - addition to those defined in section 5.1 of [RFC6749]: + Note that the AS decides which token type and profile to use when + issuing a successful response. It is assumed that the AS has prior + knowledge of the capabilities of the client, and the RS. This prior + knowledge may, for example, be set by the use of a dynamic client + registration protocol exchange [RFC7591]. + + The content of the successful reply MUST be encoded as CBOR map, + containing paramters as speficied in section 5.1 of [RFC6749]. In + addition to these parameters, the following parameters are also part + of a successful response: profile REQUIRED. This indicates the profile that the client MUST use - towards the RS. See Section 6.4 for the formatting of this + towards the RS. See Section 6.4.4 for the formatting of this parameter. cnf - REQUIRED. This field contains information about the proof-of - possession key for this access token. See Section 6.4 for the + REQUIRED if the token type is 'pop'. OPTIONAL otherwise. If a + symmetric proof-of-possession algorithms was selected, this field + contains the proof-of-possession key. If an asymmetric algorithm + was selected, this field contains information about the public key + used by the RS to authenticate. See Section 6.4.5 for the formatting of this parameter. + token_type + OPTIONAL. By default implementations of this framework SHOULD + assume that the token_type is 'pop'. If a specific use case + requires another token_type (e.g. 'Bearer') to be used then this + parameter is REQUIRED. - Note that the access token can also contains a 'cnf' claim, however, - these two values are consumed by different parties. The access token - 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. + Note that if CBOR Web Tokens [I-D.ietf-ace-cbor-web-token] are used, + the access token can also contain a 'cnf' claim. This claim is + however consumed by a different party. The access token is created + by the AS and processed by the RS (and opaque to the client) whereas + the RS Information is created by the AS and processed by the client; + it is never forwarded to the resource server. The following examples illustrate different types of responses for proof-of-possession tokens. Figure 5 shows a response containing a token and a 'cnf' parameter - with a symmetric proof-of-possession key. + with a symmetric proof-of-possession key. Note that we assume a + DTLS-based communication security profile for this example, therefore + the Content-Type is "application/cbor". Header: Created (Code=2.01) Content-Type: "application/cbor" Payload: { "access_token" : b64'SlAV32hkKG ... (remainder of CWT omitted for brevity; CWT contains COSE_Key in the 'cnf' claim)', - "token_type" : "pop", - "alg" : "HS256", "expires_in" : "3600", - "profile" : "coap_dtls" "cnf" : { "COSE_Key" : { "kty" : "Symmetric", "kid" : b64'39Gqlw', "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh' } } } Figure 5: Example AS response with an access token bound to a symmetric key. 6.3. Error Response The error responses for CoAP-based interactions with the AS are equivalent to the ones for HTTP-based interactions as defined in section 5.2 of [RFC6749], with the following differences: The - Content-Type MUST be set to "application/cbor", the payload MUST be - encoded in a CBOR map and the CoAP response code 4.00 Bad Request - MUST be used unless specified otherwise. + Content-Type is specified by the communication security profile used + between client and AS. The raw payload before being processed by the + communication security protocol MUST be encoded as a CBOR map and the + CoAP response code 4.00 (Bad Request) MUST be used unless specified + otherwise. 6.4. New Request and Response Parameters - 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. + This section provides more detail about the new parameters that can + be used in access token requests and responses, as well as + abbreviations for more compact encoding of existing parameters and + common parameter values. -6.4.1. Grant Type +6.4.1. Audience + + This parameter specifies for which audience the client is requesting + a token. It should be encoded as CBOR text string (major type 3). + + The formatting and semantics of these strings are application + specific. + +6.4.2. Grant Type The abbreviations in Figure 6 MAY be used in CBOR encodings instead of the string values defined in [RFC6749]. /--------------------+----------+--------------\ | grant_type | CBOR Key | Major Type | |--------------------+----------+--------------| | password | 0 | 0 (uint) | | authorization_code | 1 | 0 | | client_credentials | 2 | 0 | | refresh_token | 3 | 0 | \--------------------+----------+--------------/ Figure 6: CBOR abbreviations for common grant types -6.4.2. Token Type and Algorithms - - To allow clients to indicate support for specific token types and - respective algorithms they need to interact with the AS. They can - either provide this information out-of-band or via the 'token_type' - and 'alg' parameter in the client request. +6.4.3. Token Type - 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. The token type refers to the - specification used by the client to interact with the resource server - 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. + The 'token_type' parameter allows the AS to indicate to the client + which type of access token it is receiving (e.g. a bearer token). + The 'pop' token type MUST be assumed by default if the AS does not + provide a different value. This document registers the new value "pop" for the OAuth Access Token Types registry, specifying a Proof-of-Possession token. How - the proof-of-possession is performed is specified by the 'alg' - parameter. Profiles of this framework are responsible for defining - values for the 'alg' parameter together with the corresponding proof- - of-possession mechanisms. - - The values in the 'alg' parameter are case-sensitive. If the client - supports more than one algorithm then each individual value MUST be - separated by a space. - -6.4.3. Profile + the proof-of-possession is performed is specified by the profiles. - The "profile" parameter identifies the communication protocol and the - communication security protocol between the client and the RS. + The values in the 'token_type' parameter are CBOR text strings (major + type 3). - An initial set of profile identifiers and their CBOR encodings are - specified in Figure 7. Profiles using other combinations of - protocols are expected to define their own profile identifiers. +6.4.4. Profile - /--------------------+----------+--------------\ - | Profile identifier | CBOR Key | Major Type | - |--------------------+----------+--------------| - | http_tls | 0 | 0 (uint) | - | coap_dtls | 1 | 0 | - | coap_oscoap | 2 | 0 | - \--------------------+----------+--------------/ + Profiles of this framework are expected to define the communication + protocol and the communication security protocol between the client + and the RS. Furthermore profiles are expected to define proof-of- + possession methods, if they support proof-of-possession tokens. - Figure 7: Profile identifiers and their CBOR mappings + A profile should specify an identifier that is used to uniquely + identify itself in the 'profile' parameter. Profiles MAY define additional parameters for both the token request - and the client information in the access token response in order to + and the RS Information in the access token response in order to support negotioation or signalling of profile specific parameters. -6.4.4. Confirmation +6.4.5. Confirmation The "cnf" parameter identifies or provides the key used for proof-of- - 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. + possession or for authenticating the RS depending on the proof-of- + possession algorithm and the context cnf is used in. This framework + extends the definition of 'cnf' from [RFC7800] by adding CBOR/COSE + encodings and the use of 'cnf' for transporting keys in the RS + Information. A CBOR encoded payload MAY contain the 'cnf' parameter with the following contents: COSE_Key In this case the 'cnf' parameter contains the proof-of- possession key to be used by the client. An example is shown in - Figure 8. + Figure 7. "cnf" : { "COSE_Key" : { "kty" : "EC", "kid" : h'11', "crv" : "P-256", "x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8', "y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4' } } - Figure 8: Confirmation parameter containing a public key + Figure 7: Confirmation parameter containing a public key + Note that the COSE_Key structure may contain an "alg" or "key_ops" + parameter. If such parameters are present, a client MUST NOT use + a key that is not compatible with the profile or proof-of- + possession algorithm according to those parameters. COSE_Encrypted In this case the 'cnf' parameter contains an - encrypted symmetriic key destined for the client. The client is + encrypted symmetric key destined for the client. The client is 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 + COSE_Key object. Figure 8 shows an example of this type of encoding. "cnf" : { "COSE_Encrypted" : { 993( [ h'a1010a' # protected header : {"alg" : "AES-CCM-16-64-128"} "iv" : b64'ifUvZaHFgJM7UmGnjA', # unprotected header b64'WXThuZo6TMCaZZqi6ef/8WHTjOdGk8kNzaIhIQ' # ciphertext ] ) } } - Figure 9: Confirmation paramter containing an encrypted symmetric key + Figure 8: Confirmation paramter containing an encrypted symmetric key The ciphertext here could e.g. contain a symmetric key as in - Figure 10. + Figure 9. { "kty" : "Symmetric", "kid" : b64'39Gqlw', "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh' } - Figure 10: Example plaintext of an encrypted cnf parameter + Figure 9: Example plaintext of an encrypted cnf parameter Key Identifier In this case the 'cnf' parameter references a key that is assumed to be previously known by the recipient. This allows clients that perform repeated requests for an access token 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. + Figure 10 shows such an example. "cnf" : { "kid" : b64'39Gqlw' } - Figure 11: A Confirmation parameter with just a key identifier + Figure 10: A Confirmation parameter with just a key identifier 6.5. Mapping parameters to CBOR 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 | - \---------------+--------------+-----------------/ + | aud | 3 | 3 | + | client_id | 8 | 3 (text string) | + | client_secret | 9 | 2 (byte string) | + | response_type | 10 | 3 | + | redirect_uri | 11 | 3 | + | scope | 12 | 3 | + | state | 13 | 3 | + | code | 14 | 2 | + | error_description | 15 | 3 | + | error_uri | 16 | 3 | + | grant_type | 17 | 0 (unit) | + | access_token | 18 | 3 | + | token_type | 19 | 0 | + | expires_in | 20 | 0 | + | username | 21 | 3 | + | password | 22 | 3 | + | refresh_token | 23 | 3 | + | cnf | 24 | 5 (map) | + | profile | 25 | 3 | + \-------------------+----------+-----------------/ - Figure 12: CBOR mappings used in token requests + Figure 11: CBOR mappings used in token requests -7. The 'Introspect' Resource +7. The 'Introspect' Endpoint 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 + Communication between the RS and the introspection endpoint at the AS MUST be integrity protected and encrypted. Furthermore AS and RS - MUST perform mutual authentication. Finally the AS SHOULD to verify + MUST perform mutual authentication. Finally the AS SHOULD 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 RS sends a CoAP POST request to the introspection endpoint at the + AS, the profile is expected to specify the Content-Type and wrapping + of the payload. The payload MUST be encoded as 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. + For example, Figure 12 shows a RS calling the token introspection + endpoint at the AS to query about an OAuth 2.0 proof-of-possession + token. Note that we assume a object security-based communication + security profile for this example, therefore the Content-Type is + "application/cose+cbor". Header: POST (Code=0.02) Uri-Host: "server.example.com" Uri-Path: "introspect" - Content-Type: "application/cbor" + Content-Type: "application/cose+cbor" Payload: { "token" : b64'7gj0dXJQ43U', "token_type_hint" : "pop" } - Figure 13: Example introspection request. + Figure 12: 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: + If the introspection request is authorized and successfully + processed, the AS sends a response with the CoAP response code 2.01 + (Created). If the introspection request was invalid, not authorized + or couldn't be processed the AS returns an error response as + described in Section 7.3. - alg - OPTIONAL. See Section 6.4 for more details. + In a successful response, the AS encodes the response parameters in a + CBOR map including with the same required and optional parameters as + in section 2.2. of RFC 7662 [RFC7662] with the following additions: 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' + Section 6.4.5 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. + the client. See Section 6.4.4 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. + For example, Figure 13 shows an AS response to the introspection + request in Figure 12. Note that we assume a DTLS-based communication + security profile for this example, therefore the Content-Type is + "application/cbor". Header: Created Code=2.01) Content-Type: "application/cbor" Payload: { "active" : true, "scope" : "read", - "token_type" : "pop", - "alg" : "HS256", "profile" : "coap_dtls", "client_token" : b64'2QPhg0OhAQo ... (remainder of client token omitted for brevity)', "cnf" : { "COSE_Key" : { "kty" : "Symmetric", "kid" : b64'39Gqlw', "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh' } } } - Figure 14: Example introspection response. + Figure 13: Example introspection response. 7.3. Error Response The error responses for CoAP-based interactions with the AS are equivalent to the ones for HTTP-based interactions as defined in section 2.3 of [RFC7662], with the following differences: - o If content is sent, the Content-Type MUST be set to "application/ - cbor", and the payload MUST be encoded in a CBOR map. + o If content is sent, the Content-Type MUST be set according to the + specification of the communication security profile, and the + content payload MUST be encoded as 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 + with the CoAP response 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. Note that a properly formed and authorized query for an inactive or 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". @@ -1108,149 +1138,164 @@ EDITORIAL NOTE: We have tentatively introduced this concept and would specifically like feedback if this is viewed as a useful addition to the framework. 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. + Figure 14. Resource Authorization Client Server Server | | | | | | - A: +--------------->| | + C: +--------------->| | | POST | | | Access Token | | - | B: +--------------->| + | D: +--------------->| | | Introspection | | | Request | | | | - | C: +<---------------+ + | E: +<---------------+ | | Introspection | | | Response | | | + Client Token | - D: |<---------------+ | + |<---------------+ | | 2.01 Created | | | + Client Token | - Figure 15: Use of the client_token parameter. + Figure 14: Use of the client_token parameter. The client token is a COSE_Encrytped object, containing as payload a CBOR map with the following claims: cnf - REQUIRED. Contains information about the proof-of-possession key - the client is to use with its access token. See Section 6.4.4. + REQUIRED if the token type is 'pop', OPTIONAL otherwise. Contains + information about the proof-of-possession key the client is to use + with its access token. See Section 6.4.5. token_type - OPTIONAL. See Section 6.4.2. - - alg - OPTIONAL. See Section 6.4.2. + OPTIONAL. See Section 6.4.3. profile - REQUIRED. See Section 6.4.3. + REQUIRED. See Section 6.4.4. rs_cnf OPTIONAL. Contains information about the key that the RS uses to authenticate towards the client. If the key is symmetric then this claim MUST NOT be part of the Client Token, since this is the same key as the one specified through the 'cnf' claim. This claim - uses the same encoding as the 'cnf' parameter. See Section 6.4.3. + uses the same encoding as the 'cnf' parameter. See Section 6.4.4. The AS encrypts this token using a key shared between the AS and the client, so that only the client can decrypt it and access its payload. How this key is established is out of scope of this framework. 7.5. Mapping Introspection parameters to CBOR The introspection request and response parameters are mapped to CBOR types as follows and are given an integer key value to save space. - /----------------+----------+-----------------\ + /-----------------+----------+-----------------\ | 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 | - \----------------+----------+-----------------/ + |-----------------+----------+-----------------| + | iss | 1 | 3 (text string) | + | sub | 2 | 3 | + | aud | 3 | 3 | + | exp | 4 | 6 tag value 1 | + | nbf | 5 | 6 tag value 1 | + | iat | 6 | 6 tag value 1 | + | cti | 7 | 2 (byte string) | + | client_id | 8 | 3 | + | scope | 12 | 3 | + | token_type | 19 | 3 | + | username | 21 | 3 | + | cnf | 24 | 5 (map) | + | profile | 25 | 0 (uint) | + | token | 26 | 3 | + | token_type_hint | 27 | 3 | + | active | 28 | 0 | + | client_token | 29 | 3 | + | rs_cnf | 30 | 5 | + \-----------------+----------+-----------------/ - Figure 16: CBOR Mappings to Token Introspection Parameters. + Figure 15: CBOR Mappings to Token Introspection Parameters. 8. The Access Token This framework RECOMMENDS the use of CBOR web token (CWT) as specified in [I-D.ietf-ace-cbor-web-token]. In order to facilitate offline processing of access tokens, this - 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. + draft specifies the "cnf" and "scope" claims for CBOR web tokens. -8.1. The 'Authorization Information' Resource + The "scope" claim 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. + + The "cnf" claim follows the same rules as specified for JSON web + token in RFC7800 [RFC7800], except that it is encoded in CBOR in the + same way as specified for the "cnf" parameter in section + Section 6.4.5. + +8.1. The 'Authorization Information' Endpoint The access token, containing authorization information and - information of the key used by the client, is transported to the RS - so that the RS can authenticate and authorize the client request. + information of the key used by the client, needs to be transported to + the RS so that the RS can authenticate and authorize the client + request. + This section defines a method for transporting the access token to - the RS using CoAP that MAY be used. An ACE profile MAY define other - methods for token transport. + the RS using CoAP. Profiles of this framework MAY define other + methods for token transport. Implementations conforming to this + framework MUST implement this method of token transportation. - 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 method consists of a /authz-info endpoint, implemented by the RS. + A client using this method MUST make a POST request to /authz-info at 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). - 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). + If the token is not valid, the RS MUST respond with the CoAP response + 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 the CoAP + response code 4.03 (Forbidden). The RS MAY make an introspection request to validate the token before responding to the POST /authz-info request. If the introspection response contains a client token (Section 7.4) then this token SHALL be included in the payload of the 2.04 (Changed) response. + Profiles are expected to specify how the /authz-info endpoint is + protected. Note that since the token contains information that allow + the client and the RS to establish a security context in the first + place, mutual authentication may not be possible at this point. + 8.2. Token Expiration Depending on the capabilities of the RS, there are various ways in which it can verify the validity of a received access token. We list the possibilities here including what functionality they require of the RS. o The token is a CWT/JWT and includes a 'exp' claim and possibly the 'nbf' claim. The RS verifies these by comparing them to values from its internal clock as defined in [RFC7519]. In this case the - RS must have a real time chip (RTC) or some other way of reliably - measuring time. + RS's internal clock must reflect the current date and time, or at + least be synchronized with the AS's clock. How this clock + synchronization would be performed is out of scope for this memo. 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 able to handle two secure sessions in parallel (C to RS and AS to 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 @@ -1262,47 +1307,91 @@ means of reliably measuring time, this is the best that can be achieved. 9. Security Considerations The entire document is about security. Security considerations applicable to authentication and authorization in RESTful environments provided in OAuth 2.0 [RFC6749] apply to this work, as well as the security considerations from [I-D.ietf-ace-actors]. 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. + OAuth which apply to IoT deployments as well. + + A large range of threats can be mitigated by protecting the contents + of the access token by using a digital signature or a keyed message + digest. Consequently, the token integrity protection MUST be applied + to prevent the token from being modified, particularly since it + contains a reference to the symmetric key or the asymmetric key. If + the access token contains the symmetric key, this symmetric key MUST + be encrypted by the authorization server with a long-term key shared + with the resource server. + + It is important for the authorization server to include the identity + of the intended recipient (the audience), typically a single resource + server (or a list of resource servers), in the token. Using a single + shared secret with multiple authorization server to simplify key + management is NOT RECOMMENDED since the benefit from using the proof- + of-possession concept is significantly reduced. + + Token replay is also not possible since an eavesdropper will also + have to obtain the corresponding private key or shared secret that is + bound to the access token. Nevertheless, it is good practice to + limit the lifetime of the access token and therefore the lifetime of + associated key. + + The authorization server MUST offer confidentiality protection for + any interactions with the client. This step is extremely important + since the client will obtain the session key from the authorization + server for use with a specific access token. Not using + confidentiality protection exposes this secret (and the access token) + to an eavesdropper thereby making the proof-of-possession security + model completely insecure. This framework relies on profiles to + define how confidentiality protection is provided, and additional + protection can be applied by encrypting the CWT as specified in + section 5.1 of [I-D.ietf-ace-cbor-web-token] to provide an additional + layer of protection for cases where keying material is conveyed, for + example, to a hardware security module. + + Developers MUST ensure that the ephemeral credentials (i.e., the + private key or the session key) is not leaked to third parties. An + adversary in possession of the ephemeral credentials bound to the + access token will be able to impersonate the client. Be aware that + this is a real risk with many constrained environments, since + adversaries can often easily get physical access to the devices. + + Clients can at any time request a new proof-of-possession capable + access token. Using a refresh token to regularly request new access + tokens that are bound to fresh and unique keys is important if the + client has this capability. Keeping the lifetime of the access token + short allows the authorization server to use shorter key sizes, which + translate to a performance benefit for the client and for the + resource server. Shorter keys also lead to shorter messages + (particularly with asymmetric keying material). + + When authorization servers bind symmetric keys to access tokens then + they SHOULD scope these access tokens to a specific permissions. 10. IANA Considerations This specification registers new parameters for OAuth and establishes registries for mappings to CBOR. 10.1. OAuth Introspection Response Parameter Registration This specification registers the following parameters in the OAuth introspection response parameters - o Name: "alg" - o Description: Algorithm to use with PoP key, as defined in PoP - token specification, - o Change Controller: IESG - o Specification Document(s): this document - o Name: "cnf" o Description: Key to use to prove the right to use an access token, as defined in [RFC7800]. o Change Controller: IESG o Specification Document(s): this document - o Name: "aud" o Description: reference to intended receiving RS, as defined in PoP token specification. o Change Controller: IESG o Specification Document(s): this document o Name: "profile" o Description: The communication and communication security profile used between client and RS, as defined in ACE profiles. o Change Controller: IESG @@ -1307,31 +1396,30 @@ used between client and RS, as defined in ACE profiles. o Change Controller: IESG o Specification Document(s): this document o Name: "client_token" o Description: Information that the RS MUST pass to the client e.g. about the proof-of-possession keys. o Change Controller: IESG o Specification Document(s): this document + o Name: "rs_cnf" + o Description: Describes the public key the RS uses to authenticate. + o Change Controller: IESG + o Specification Document(s): this document + 10.2. OAuth Parameter Registration This specification registers the following parameters in the OAuth Parameters Registry - o Name: "alg" - o Description: Algorithm to use with PoP key, as defined in PoP - token specification, - o Change Controller: IESG - o Specification Document(s): this document - o Parameter name: "profile" o Parameter usage location: token request, and token response o Change Controller: IESG o Specification Document(s): this document o Name: "cnf" o Description: Key to use to prove the right to use an access token, as defined in [RFC7800]. o Change Controller: IESG o Specification Document(s): this document @@ -1375,31 +1462,37 @@ o Parameter name: "Bearer" o Mapped value: 1 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "pop" o Mapped value: 2 o Change Controller: IESG o Specification Document(s): this document -10.5. JSON Web Token Claims +10.5. CBOR Web Token Claims - This specification registers the following new claim in the JSON Web - Token (JWT) registry. + This specification registers the following new claims in the CBOR Web + Token (CWT) registry: o Claim Name: "scope" o Claim Description: The scope of an access token as defined in [RFC6749]. o Change Controller: IESG o Specification Document(s): this document + o Claim Name: "cnf" + o Claim Description: The proof-of-possession key of an access token + as defined in [RFC7800]. + o Change Controller: IESG + o Specification Document(s): this document + 10.6. ACE Profile Registry A new registry will be requested from IANA, entitled "ACE Profile Registry". The registry is to be created as Expert Review Required. 10.6.1. Registration Template Profile name: Name of the profile to be included in the profile attribute. Profile description: @@ -1414,21 +1506,21 @@ 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. 10.7. OAuth Parameter Mappings Registry - A new registry will be requested from IANA, entitled "Token Resource + A new registry will be requested from IANA, entitled "Token Endpoint CBOR Mappings Registry". The registry is to be created as Expert Review Required. 10.7.1. Registration Template Parameter name: OAuth Parameter name, refers to the name in the OAuth parameter registry e.g. "client_id". CBOR key value: Key value for the claim. The key value MUST be an integer in the @@ -1430,132 +1522,127 @@ Parameter name: OAuth Parameter name, refers to the name in the OAuth parameter registry e.g. "client_id". 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. 10.7.2. Initial Registry Contents + o Parameter name: "aud" + o CBOR key value: 3 + o Change Controller: IESG + o Specification Document(s): this document + o Parameter name: "client_id" - o CBOR key value: 1 + o CBOR key value: 8 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "client_secret" - o CBOR key value: 2 + o CBOR key value: 9 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "response_type" - o CBOR key value: 3 + o CBOR key value: 10 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "redirect_uri" - o CBOR key value: 4 + o CBOR key value: 11 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "scope" - o CBOR key value: 5 + o CBOR key value: 12 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "state" - o CBOR key value: 6 + o CBOR key value: 13 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "code" - o CBOR key value: 7 + o CBOR key value: 14 o Change Controller: IESG o Specification Document(s): this document - o Parameter name: "error_description" - o CBOR key value: 8 + o CBOR key value: 15 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "error_uri" - o CBOR key value: 9 + o CBOR key value: 16 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "grant_type" - o CBOR key value: 10 + o CBOR key value: 17 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "access_token" - o CBOR key value: 11 + o CBOR key value: 18 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "token_type" - o CBOR key value: 12 + o CBOR key value: 19 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "expires_in" - o CBOR key value: 13 + o CBOR key value: 20 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "username" - o CBOR key value: 14 + o CBOR key value: 21 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "password" - o CBOR key value: 15 + o CBOR key value: 22 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "refresh_token" - o CBOR key value: 16 - o Change Controller: IESG - o Specification Document(s): this document - - o Parameter name: "alg" - o CBOR key value: 17 + o CBOR key value: 23 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "cnf" - o CBOR key value: 18 - o Change Controller: IESG - o Specification Document(s): this document - - o Parameter name: "aud" - o CBOR key value: 19 + o CBOR key value: 24 o Change Controller: IESG o Specification Document(s): this document o Parameter name: "profile" - o CBOR key value: 20 + o CBOR key value: 25 o Change Controller: IESG o Specification Document(s): this document -10.8. Introspection Resource CBOR Mappings Registry +10.8. Introspection Endpoint CBOR Mappings Registry A new registry will be requested from IANA, entitled "Introspection - Resource CBOR Mappings Registry". The registry is to be created as + Endpoint CBOR Mappings Registry". The registry is to be created as Expert Review Required. 10.8.1. Registration Template 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. @@ -1564,92 +1651,106 @@ 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. 10.8.2. Initial Registry Contents - o Response parameter name: "active" + o Response parameter name: "iss" o CBOR key value: 1 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "username" + o Response parameter name: "sub" o CBOR key value: 2 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "client_id" + o Response parameter name: "aud" o CBOR key value: 3 o Change Controller: IESG o Specification Document(s): this document - - o Response parameter name: "scope" + o Response parameter name: "exp" o CBOR key value: 4 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "token_type" + o Response parameter name: "nbf" o CBOR key value: 5 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "exp" + o Response parameter name: "iat" o CBOR key value: 6 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "iat" + o Response parameter name: "cti" o CBOR key value: 7 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "nbf" + o Response parameter name: "client_id" o CBOR key value: 8 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "sub" - o CBOR key value: 9 + o Response parameter name: "scope" + o CBOR key value: 12 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "aud" - o CBOR key value: 10 + o Response parameter name: "token_type" + o CBOR key value: 19 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "iss" - o CBOR key value: 11 + o Response parameter name: "username" + o CBOR key value: 21 o Change Controller: IESG o Specification Document(s): this document - o Response parameter name: "jti" - o CBOR key value: 12 + o Parameter name: "cnf" + o CBOR key value: 24 o Change Controller: IESG o Specification Document(s): this document - o Parameter name: "alg" - o CBOR key value: 13 + o Parameter name: "profile" + o CBOR key value: 25 o Change Controller: IESG o Specification Document(s): this document - o Parameter name: "cnf" - o CBOR key value: 14 + o Response parameter name: "token" + o CBOR key value: 26 o Change Controller: IESG o Specification Document(s): this document - o Parameter name: "aud" - o CBOR key value: 15 + o Response parameter name: "token_type_hint" + o CBOR key value: 27 + o Change Controller: IESG + o Specification Document(s): this document + + o Response parameter name: "active" + o CBOR key value: 28 + o Change Controller: IESG + o Specification Document(s): this document + + o Response parameter name: "client_token" + o CBOR key value: 29 + o Change Controller: IESG + o Specification Document(s): this document + + o Response parameter name: "rs_cnf" + o CBOR key value: 30 o Change Controller: IESG o Specification Document(s): this document 10.9. CoAP Option Number Registration This section registers the "Access-Token" CoAP Option Number in the "CoRE Parameters" sub-registry "CoAP Option Numbers" in the manner described in [RFC7252]. Name @@ -1659,62 +1760,60 @@ TBD Reference [This document]. Meaning in Request Contains an Access Token according to [This document] containing access permissions of the client. Meaning in Response - Not used in response Safe-to-Forward - TBD + Yes Format Based on the observer the format is perceived differently. Opaque data to the client and CWT or reference token to the RS. Length Less then 255 bytes 11. Acknowledgments 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 input, and Malisa Vucinic for his input on the ACRE proposal [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 general for their feedback. + We would like to thank the authors of draft-ietf-oauth-pop-key- + distribution, from where we copied large parts of our security + considerations. + Ludwig Seitz and Goeran Selander worked on this document as part of the CelticPlus project CyberWI, with funding from Vinnova. 12. References 12.1. Normative References [I-D.ietf-ace-cbor-web-token] - Wahlstroem, E., Jones, M., and H. Tschofenig, "CBOR Web - Token (CWT)", draft-ietf-ace-cbor-web-token-00 (work in - progress), May 2016. + Wahlstroem, E., Jones, M., Tschofenig, H., and S. Erdtman, + "CBOR Web Token (CWT)", draft-ietf-ace-cbor-web-token-01 + (work in progress), July 2016. [I-D.ietf-cose-msg] - Schaad, J., "CBOR Encoded Message Syntax", draft-ietf- - cose-msg-12 (work in progress), May 2016. - - [I-D.selander-ace-object-security] - Selander, G., Mattsson, J., Palombini, F., and L. Seitz, - "Object Security of CoAP (OSCOAP)", draft-selander-ace- - object-security-04 (work in progress), March 2016. + Schaad, J., "CBOR Object Signing and Encryption (COSE)", + draft-ietf-cose-msg-19 (work in progress), September 2016. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, . @@ -1730,38 +1829,43 @@ [RFC7800] Jones, M., Bradley, J., and H. Tschofenig, "Proof-of- Possession Key Semantics for JSON Web Tokens (JWTs)", RFC 7800, DOI 10.17487/RFC7800, April 2016, . 12.2. Informative References [I-D.ietf-ace-actors] Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An architecture for authorization in constrained - environments", draft-ietf-ace-actors-03 (work in - progress), March 2016. + environments", draft-ietf-ace-actors-04 (work in + progress), September 2016. - [I-D.ietf-core-block] - Bormann, C. and Z. Shelby, "Block-wise transfers in CoAP", - draft-ietf-core-block-20 (work in progress), April 2016. + [I-D.ietf-oauth-device-flow] + Denniss, W., Myrseth, S., Bradley, J., Jones, M., and H. + Tschofenig, "OAuth 2.0 Device Flow", draft-ietf-oauth- + device-flow-03 (work in progress), July 2016. - [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-native-apps] + Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps", + draft-ietf-oauth-native-apps-03 (work in progress), July + 2016. [I-D.seitz-ace-core-authz] Seitz, L., Selander, G., and M. Vucinic, "Authorization for Constrained RESTful Environments", draft-seitz-ace- core-authz-00 (work in progress), June 2015. + [I-D.selander-ace-object-security] + Selander, G., Mattsson, J., Palombini, F., and L. Seitz, + "Object Security of CoAP (OSCOAP)", draft-selander-ace- + object-security-05 (work in progress), July 2016. + [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, . [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, . [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link @@ -1792,31 +1896,41 @@ [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014, . [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, . + [RFC7521] Campbell, B., Mortimore, C., Jones, M., and Y. Goland, + "Assertion Framework for OAuth 2.0 Client Authentication + and Authorization Grants", RFC 7521, DOI 10.17487/RFC7521, + May 2015, . + [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, . [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, . + [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in + the Constrained Application Protocol (CoAP)", RFC 7959, + DOI 10.17487/RFC7959, August 2016, + . + Appendix A. Design Justification This section provides further insight into the design decisions of the solution documented in this document. Section 3 lists several building blocks and briefly summarizes their importance. The justification for offering some of those building blocks, as opposed to using OAuth 2.0 as is, is given below. Common IoT constraints are: @@ -1883,95 +1997,100 @@ security reasons, e.g. to avoid an entry point for Denial-of- Service attacks. The communication interactions this framework builds upon (as shown graphically in Figure 1) may be accomplished using a variety of different protocols, and not all parts of the message flow are used in all applications due to the communication constraints. While we envision deployments to make use of CoAP we explicitly want to support HTTP, HTTP/2 or specific protocols, such as Bluetooth Smart communication, which does not necessarily use IP. + The latter raises the need for application layer security over the various interfaces. Appendix B. Roles and Responsibilites Resource Owner - * Make sure that the RS is registered at the AS. + * Make sure that the RS is registered at the AS. This includes + making known to the AS which profiles, token_types, scopes, and + key types (symmetric/asymmetric) the RS supports. Also making + it known to the AS which audience(s) the RS identifies itself + with. * Make sure that clients can discover the AS which is in charge of the RS. * Make sure that the AS has the necessary, up-to-date, access control policies for the RS. Requesting Party * Make sure that the client is provisioned the necessary credentials to authenticate to the AS. * Make sure that the client is configured to follow the security requirements of the Requesting Party, when issuing requests (e.g. minimum communication security requirements, trust anchors). - * Register the client at the AS. + * Register the client at the AS. This includes making known to + the AS which profiles, token_types, and key types (symmetric/ + asymmetric) the client. Authorization Server * Register RS and manage corresponding security contexts. * Register clients and including authentication credentials. * Allow Resource Owners to configure and update access control policies related to their registered RS' - * Expose a service that allows clients to request tokens. - * Authenticate clients that wishes to request a token. - * Process a token requests against the authorization policies + * Expose the /token endpoint to allow clients to request tokens. + * Authenticate clients that wish to request a token. + * Process a token request against the authorization policies configured for the RS. - * Expose a service that allows RS's to submit token introspection - requests. - * Authenticate RS's that wishes to get an introspection response. + * Expose the /introspection endpoint that allows RS's to submit + token introspection requests. + * Authenticate RS's that wish to get an introspection response. * Process token introspection requests. * Optionally: Handle token revocation. Client - * Discover the AS in charge of the RS that is to be targeted with a request. * Submit the token request (A). + Authenticate towards the AS. - + Specify which RS, which resource(s), and which action(s) the - request(s) will target. - + Specify preferences for communication security + + Optionally (if not pre-configured): Specify which RS, which + resource(s), and which action(s) the request(s) will target. + If raw public key (rpk) or certificate is used, make sure the AS has the right rpk or certificate for this client. - * Process the access token and client information (B) + * Process the access token and RS Information (B) - + Check that the token has the right format (e.g. CWT). - + Check that the client information provides the necessary + + Check that the RS Information provides the necessary security parameters (e.g. PoP key, information on communication security protocols supported by the RS). * Send the token and request to the RS (C) + Authenticate towards the RS (this could coincide with the proof of possession process). - + Transmit the token as specified by the AS (default is to an - authorization information resource, alternative options are - as a CoAP option or in the DTLS handshake). - + Perform the proof-of-possession procedure as specified for - the type of used token (this may already have been taken - care of through the authentication procedure). + + Transmit the token as specified by the AS (default is to the + /authz-info endpoint, alternative options are specified by + profiles). + + Perform the proof-of-possession procedure as specified by + the profile in use (this may already have been taken care of + through the authentication procedure). * Process the RS response (F) requirements of the Requesting Party, when issuing requests (e.g. minimum communication security requirements, trust anchors). * Register the client at the AS. Resource Server - * Expose a way to submit access tokens. + * Expose a way to submit access tokens. By default this is the + /authz-info endpoint. * Process an access token. + Verify the token is from the right AS. + Verify that the token applies to this RS. + Check that the token has not expired (if the token provides expiration information). + Check the token's integrity. + Store the token so that it can be retrieved in the context of a matching request. * Process a request. @@ -1970,104 +2089,141 @@ + Verify the token is from the right AS. + Verify that the token applies to this RS. + Check that the token has not expired (if the token provides expiration information). + Check the token's integrity. + Store the token so that it can be retrieved in the context of a matching request. * Process a request. + Set up communication security with the client. - + Authenticate the client. + Match the client against existing tokens. + + Check that tokens belonging to the client actually authorize the requested action. + 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 security. -Appendix C. Deployment Examples +Appendix C. Requirements on Profiles + + This section lists the requirements on profiles of this framework, + for the convenience of a profile designer. All this information is + also given in the appropriate sections of the main document, this is + just meant as a checklist, to make it more easy to spot parts one + might have missed. + + o Specify the discovery process of how the client finds the right AS + for an RS it wants to send a request to. + o Specify the communication protocol the client and RS the must use + (e.g. CoAP). + o Specify the security protocol the client and RS must use to + protect their communication (e.g. OSCOAP or DTLS over CoAP). + This must provide encryption and integrity protection. + o Specify how the client and the RS mutually authenticate + o Specify the Content-format of the protocol messages (e.g. + "application/cbor" or "application/cose+cbor"). + o Specify the proof-of-possession protocol(s) and how to select one, + if several are available. Also specify which key types (e.g. + symmetric/asymmetric) are supported by a specific proof-of- + possession protocol. + o Specify a unique profile identifier. + o Optionally specify how the RS talks to the AS for introspection. + o Optionally specify how the client talks to the AS for requesting a + token. + o Specify how/if the /authz-info endpoint is protected. + o Optionally define other methods of token transport than the + /authz-info endpoint. + +Appendix D. Deployment Examples There is a large variety of IoT deployments, as is indicated in Appendix A, and this section highlights a few common variants. This section is not normative but illustrates how the framework can be applied. 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. Note: CBOR diagnostic notation is used for examples of requests and responses. -C.1. Local Token Validation +D.1. Local Token Validation In this scenario we consider the case where the resource server is offline, i.e. it is not connected to the AS at the time of the access request. This access procedure involves steps A, B, C, and F of Figure 1. Since the resource server must be able to verify the access token locally, self-contained access tokens must be used. 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. + server. Message exchanges A and B are shown in Figure 16. A: The client first generates a public-private key pair used for communication security with the RS. The client sends the POST request to /token at the AS. The - request contains the public key of the client and the Audience - 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. - - B: The AS responds with a PoP token and client information. The - PoP token contains the public key of the client, and the client - information contains the public key of the RS. For communication + security of this request can be transport or application layer, it + is up the the comunication security profile to define. In the + example trasport layer identification of the AS is done and the + client identifies with client_id and client_secret as in classic + OAuth. The request contains the public key of the client and the + Audience 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. + B: The AS responds with a PoP token and RS Information. The PoP + token contains the public key of the client, and the RS + 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. + i.e. 'exp' close to 'iat', to protect the RS from replay attacks. + The token includes the claim such as "scope" with the authorized + access that an owner of the temperature device can enjoy. In this + example, the 'scope' 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 that the + syntax and semantics of the scope claim are application specific. 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. Authorization Client Server | | + |<=======>| DTLS Connection Establishment + | | to identify the AS | | A: +-------->| Header: POST (Code=0.02) | POST | Uri-Path:"token" | | Content-Type: application/cbor | | Payload: | | B: |<--------+ Header: 2.05 Content | 2.05 | Content-Type: application/cbor | | Payload: | | - Figure 17: Token Request and Response Using Client Credentials. + Figure 16: Token Request and Response Using Client Credentials. The information contained in the Request-Payload and the Response- - Payload is shown in Figure 18. + Payload is shown in Figure 17. Note that we assume a DTLS-based + communication security profile for this example, therefore the + Content-Type is "application/cbor". Request-Payload : { "grant_type" : "client_credentials", "aud" : "tempSensorInLivingRoom", "client_id" : "myclient", "client_secret" : "qwerty" } Response-Payload : @@ -2079,67 +2235,68 @@ "COSE_Key" : { "kid" : b64'c29tZSBwdWJsaWMga2V5IGlk', "kty" : "EC", "crv" : "P-256", "x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4', "y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM' } } } - Figure 18: Request and Response Payload Details. + Figure 17: Request and Response Payload Details. - The content of the access token is shown in Figure 19. + The content of the access token is shown in Figure 18. { "aud" : "tempSensorInLivingRoom", "iat" : "1360189224", "exp" : "1360289224", - "aif" : [["/temperature", 0], ["/firmware", 2]], + "scope" : "temperature_g firmware_p", "cnf" : { "jwk" : { "kid" : b64'1Bg8vub9tLe1gHMzV76e8', "kty" : "EC", "crv" : "P-256", "x" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU', "y" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0' } } } - Figure 19: Access Token including Public Key of the Client. + Figure 18: Access Token including Public Key of the Client. - Messages C and F are shown in Figure 20 - Figure 21. + Messages C and F are shown in Figure 19 - Figure 20. - C: The client then sends the PoP token to the /authz-info resource + C: The client then sends the PoP token to the /authz-info endpoint at the RS. This is a plain CoAP request, i.e. no transport or application layer security between client and RS, since the token is integrity protected 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. Resource Client Server | | C: +-------->| Header: POST (Code=0.02) | POST | Uri-Path:"authz-info" | | Payload: SlAV32hkKG ... | | - |<--------+ Header: 2.01 Created - | 2.01 | + |<--------+ Header: 2.04 Changed + | 2.04 | | | - Figure 20: Access Token provisioning to RS + Figure 19: 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. Resource Client Server | | |<=======>| DTLS Connection Establishment | | using Raw Public Keys @@ -2146,42 +2303,42 @@ | | +-------->| Header: GET (Code=0.01) | GET | Uri-Path: "temperature" | | | | | | F: |<--------+ Header: 2.05 Content | 2.05 | Payload: | | - Figure 21: Resource Request and Response protected by DTLS. + Figure 20: Resource Request and Response protected by DTLS. -C.2. Introspection Aided Token Validation +D.2. Introspection Aided Token Validation - In this deployment scenario we assume that a client is not be able to + In this deployment scenario we assume that a client is not 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. Since the client is assumed to be offline, at least for a certain 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. - 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. + In the example interactions between an offline client (key fob), a RS + (online lock), and an AS is shown. 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 21. Authorization consent from the resource owner can be pre-configured, 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. @@ -2189,44 +2346,47 @@ 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. A: The client sends the request using POST to /token at AS. The 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. + targeted audience and a symmetric key. The security is provided + by identifying the AS on transport layer using a pre shared + security context (psk, rpk or certificate) and then the client is + identified using client_id and client_secret as in classic OAuth + B: The AS responds with the an access token and RS 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. Authorization Client Server | | | | A: +-------->| Header: POST (Code=0.02) | POST | Uri-Path:"token" | | Content-Type: application/cbor | | Payload: | | B: |<--------+ Header: 2.05 Content | | Content-Type: application/cbor | 2.05 | Payload: | | - Figure 22: Token Request and Response using Client Credentials. + Figure 21: Token Request and Response using Client Credentials. The information contained in the Request-Payload and the Response- - Payload is shown in Figure 23. + Payload is shown in Figure 22. Request-Payload: { "grant_type" : "client_credentials", "aud" : "lockOfDoor4711", "client_id" : "keyfob", "client_secret" : "qwerty" } Response-Payload: @@ -2237,89 +2397,91 @@ "cnf" : { "COSE_Key" : { "kid" : b64'c29tZSBwdWJsaWMga2V5IGlk', "kty" : "oct", "alg" : "HS256", "k": b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE' } } } - Figure 23: Request and Response Payload for C offline + Figure 22: Request and Response Payload for C offline The access token in this case is just an opaque string referencing the authorization information at the AS. C: Next, the client POSTs the access token to the /authz-info - resource in the RS. This is a plain CoAP request, i.e. no DTLS + endpoint in the RS. This is a plain CoAP request, i.e. no DTLS 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 + D: The RS forwards the token to the /introspect endpoint 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. + the RS, e.g. using transport of application layer security. In + the example AS is identified using pre shared security context + (psk, rpk or certificate) while RS is acting as client and is + identified with client_id and client_secret. 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. + step C with the CoAP response code 2.01 (Created). 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) + | D: +--------->| Header: POST (Code=0.02) | | POST | Uri-Path: "introspect" | | | Content-Type: "application/cbor" | | | Payload: | | | - E: | |<---------+ Header: 2.05 Content + | E: |<---------+ Header: 2.05 Content | | 2.05 | Content-Type: "application/cbor" | | | Payload: | | | | | - C: |<--------+ Header: 2.01 Created + |<--------+ Header: 2.01 Created | 2.01 | | | - Figure 24: Token Introspection for C offline + Figure 23: Token Introspection for C offline The information contained in the Request-Payload and the Response- - Payload is shown in Figure 25. + Payload is shown in Figure 24. Request-Payload: { "token" : b64'SlAV32hkKG...', "client_id" : "FrontDoor", "client_secret" : "ytrewq" } Response-Payload: { "active" : true, "aud" : "lockOfDoor4711", "scope" : "open, close", "iat" : 1311280970, "cnf" : { "kid" : b64'JDLUhTMjU2IiwiY3R5Ijoi ...' } } - Figure 25: Request and Response Payload for Introspection + Figure 24: Request and Response Payload for Introspection The client uses the symmetric PoP key to establish a DTLS 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. Resource Client Server @@ -2328,27 +2490,47 @@ | | using Pre Shared Key | | +-------->| Header: PUT (Code=0.03) | PUT | Uri-Path: "state" | | Payload: | | F: |<--------+ Header: 2.04 Changed | 2.04 | Payload: | | - Figure 26: Resource request and response protected by OSCOAP + Figure 25: Resource request and response protected by OSCOAP -Appendix D. Document Updates -D.1. Version -01 to -02 +Appendix E. Document Updates + +E.1. Version -02 to -03 + + o Removed references to draft-ietf-oauth-pop-key-distribution since + the status of this draft is unclear. + o Copied and adapted security considerations from draft-ietf-oauth- + pop-key-distribution. + o Renamed "client information" to "RS information" since it is + information about the RS. + o Clarified the requirements on profiles of this framework. + o Clarified the token endpoint protocol and removed negotiation of + 'profile' and 'alg' (section 6). + o Renumbered the abbreviations for claims and parameters to get a + consistent numbering across different endpoints. + o Clarified the introspection endpoint. + o Renamed token, introspection and authz-info to 'endpoint' instead + of 'resource' to mirror the OAuth 2.0 terminology. + o Updated the examples in the appendices. + +E.2. Version -01 to -02 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. @@ -2347,21 +2529,21 @@ 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. -D.2. Version -00 to -01 +E.3. Version -00 to -01 o Changed 5.1. from "Communication Security Protocol" to "Client Information". o Major rewrite of 5.1 to clarify the information exchanged between C and AS in the PoP token request profile for IoT. * Allow the client to indicate preferences for the communication security protocol. * Defined the term "Client Information" for the additional information returned to the client in addition to the access @@ -2399,26 +2581,23 @@ Goeran Selander Ericsson Faroegatan 6 Kista 164 80 SWEDEN Email: goran.selander@ericsson.com Erik Wahlstroem - Nexus Technology - Telefonvagen 26 - Hagersten 126 26 Sweden - Email: erik.wahlstrom@nexusgroup.com + Email: erik@wahlstromtekniska.se Samuel Erdtman Spotify AB Birger Jarlsgatan 61, 4tr Stockholm 113 56 Sweden Email: erdtman@spotify.com Hannes Tschofenig