draft-ietf-ace-dtls-authorize-04.txt		draft-ietf-ace-dtls-authorize-05.txt
	ACE Working Group S. Gerdes		ACE Working Group S. Gerdes
	Internet-Draft O. Bergmann		Internet-Draft O. Bergmann
	Intended status: Standards Track C. Bormann		Intended status: Standards Track C. Bormann
	Expires: March 10, 2019 Universitaet Bremen TZI		Expires: April 11, 2019 Universitaet Bremen TZI
	G. Selander		G. Selander
	Ericsson		Ericsson AB
	L. Seitz		L. Seitz
	RISE SICS		RISE SICS
	September 06, 2018		October 08, 2018
	Datagram Transport Layer Security (DTLS) Profile for Authentication and		Datagram Transport Layer Security (DTLS) Profile for Authentication and
	Authorization for Constrained Environments (ACE)		Authorization for Constrained Environments (ACE)
	draft-ietf-ace-dtls-authorize-04		draft-ietf-ace-dtls-authorize-05
	Abstract		Abstract
	This specification defines a profile for delegating client		This specification defines a profile that allows constrained servers
	authentication and authorization in a constrained environment by		to delegate client authentication and authorization. The protocol
	establishing a Datagram Transport Layer Security (DTLS) channel		relies on DTLS for communication security between entities in a
	between resource-constrained nodes. The protocol relies on DTLS for		constrained network using either raw public keys or pre-shared keys.
	communication security between entities in a constrained network		A resource-constrained server can use this protocol to delegate
	using either raw public keys or pre-shared keys. A resource-		management of authorization information to a trusted host with less
	constrained node can use this protocol to delegate management of		severe limitations regarding processing power and memory.
	authorization information to a trusted host with less severe
	limitations regarding processing power and memory.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on March 10, 2019.		This Internet-Draft will expire on April 11, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 25 ¶		skipping to change at page 2, line 20 ¶
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3		1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3		2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3
	2.1. Resource Access . . . . . . . . . . . . . . . . . . . . . 5		3. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 5
	2.2. Dynamic Update of Authorization Information . . . . . . . 7		3.1. Communication between C and AS . . . . . . . . . . . . . 5
	2.3. Token Expiration . . . . . . . . . . . . . . . . . . . . 8		3.2. RawPublicKey Mode . . . . . . . . . . . . . . . . . . . . 6
	3. RawPublicKey Mode . . . . . . . . . . . . . . . . . . . . . . 9		3.2.1. DTLS Channel Setup Between C and RS . . . . . . . . . 7
	4. PreSharedKey Mode . . . . . . . . . . . . . . . . . . . . . . 10		3.3. PreSharedKey Mode . . . . . . . . . . . . . . . . . . . . 8
	4.1. DTLS Channel Setup Between C and RS . . . . . . . . . . . 12		3.3.1. DTLS Channel Setup Between C and RS . . . . . . . . . 10
	4.2. Updating Authorization Information . . . . . . . . . . . 13		3.4. Resource Access . . . . . . . . . . . . . . . . . . . . . 12
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 14		4. Dynamic Update of Authorization Information . . . . . . . . . 13
	6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 14		5. Token Expiration . . . . . . . . . . . . . . . . . . . . . . 14
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14		6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15		7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 15
	8.1. Normative References . . . . . . . . . . . . . . . . . . 15		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
	8.2. Informative References . . . . . . . . . . . . . . . . . 16		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
	8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 17		9.1. Normative References . . . . . . . . . . . . . . . . . . 16
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18		9.2. Informative References . . . . . . . . . . . . . . . . . 17
			9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 18
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
	1. Introduction		1. Introduction
	This specification defines a profile of the ACE framework		This specification defines a profile of the ACE framework
	[I-D.ietf-ace-oauth-authz]. In this profile, a client and a resource		[I-D.ietf-ace-oauth-authz]. In this profile, a client and a resource
	server use CoAP [RFC7252] over DTLS [RFC6347] to communicate. The		server use CoAP [RFC7252] over DTLS [RFC6347] to communicate. The
	client uses an access token, bound to a key (the proof-of-possession		client obtains an access token, bound to a key (the proof-of-
	key) to authorize its access to protected resources hosted by the		possession key), from an authorization server to prove its
	resource server. DTLS provides communication security, proof of		authorization to access protected resources hosted by the resource
	possession, and server authentication. Optionally the client and the		server. Also, the client and the resource server are provided by the
	resource server may also use CoAP over DTLS to communicate with the		authorization server with the necessary keying material to establish
	authorization server. This specification supports the DTLS handshake		a DTLS session. The communication between client and authorization
	with Raw Public Keys (RPK) [RFC7250] and the DTLS handshake with Pre-		server may also be secured with DTLS. This specification supports
	Shared Keys (PSK) [RFC4279].		DTLS with Raw Public Keys (RPK) [RFC7250] and with Pre-Shared Keys
			(PSK) [RFC4279].
	The DTLS RPK handshake [RFC7250] requires client authentication to		The DTLS handshake [RFC7250] requires the client and server to prove
	provide proof-of-possession for the key tied to the access token.		that they can use certain keying material. In the RPK mode, the
	Here the access token needs to be transferred to the resource server		client proves with the DTLS handshake that it can use the RPK bound
	before the handshake is initiated, as described in section 5.8.1 of		to the token and the server shows that it can use a certain RPK. The
			access token must be presented to the resource server. For the RPK
			mode, the access token needs to be uploaded to the resource server
			before the handshake is initiated, as described in Section 5.8.1 of
	draft-ietf-ace-oauth-authz [1].		draft-ietf-ace-oauth-authz [1].
	The DTLS PSK handshake [RFC4279] provides the proof-of-possession for		In the PSK mode, client and server show with the DTLS handshake that
	the key tied to the access token. Furthermore the psk_identity		they can use the keying material that is bound to the access token.
	parameter in the DTLS PSK handshake is used to transfer the access		To transfer the access token from the client to the resource server,
	token from the client to the resource server.		the "psk_identity" parameter in the DTLS PSK handshake may be used
			instead of uploading the token prior to the handshake.
	1.1. Terminology		1.1. Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	Readers are expected to be familiar with the terms and concepts		Readers are expected to be familiar with the terms and concepts
	described in [I-D.ietf-ace-oauth-authz].		described in I-D.ietf-ace-oauth-authz [2].
			The authz-info resource refers to the authz-info endpoint as
			specified in I-D.ietf-ace-oauth-authz [3].
	2. Protocol Overview		2. Protocol Overview
	The CoAP-DTLS profile for ACE specifies the transfer of		The CoAP-DTLS profile for ACE specifies the transfer of
	authentication and, if necessary, authorization information between		authentication information and, if necessary, authorization
	the client C and the resource server RS during setup of a DTLS		information between the client (C) and the resource server (RS)
	session for CoAP messaging. It also specifies how a Client can use		during setup of a DTLS session for CoAP messaging. It also specifies
	CoAP over DTLS to retrieve an Access Token from the authorization		how C can use CoAP over DTLS to retrieve an access token from the
	server AS for a protected resource hosted on the resource server RS.		authorization server (AS) for a protected resource hosted on the
			resource server.
	This profile requires a Client (C) to retrieve an Access Token for		This profile requires the client to retrieve an access token for
	the resource(s) it wants to access on a Resource Server (RS) as		protected resource(s) it wants to access on RS as specified in I-
	specified in [I-D.ietf-ace-oauth-authz]. Figure 1 shows the typical		D.ietf-ace-oauth-authz [4]. Figure 1 shows the typical message flow
	message flow in this scenario (messages in square brackets are		in this scenario (messages in square brackets are optional):
	optional):
	C RS AS		C RS AS
	| [-- Resource Request --->] | |		| [-- Resource Request --->] | |
	| | |		| | |
	| [<----- AS Information --] | |		| [<----- AS Information --] | |
	| | |		| | |
	| --- Token Request ----------------------------> |		| --- Token Request ----------------------------> |
	| | |		| | |
	| <---------------------------- Access Token ----- |		| <---------------------------- Access Token ----- |
	| + RS Information |		| + Access Information |
	Figure 1: Retrieving an Access Token		Figure 1: Retrieving an Access Token
	To determine the AS in charge of a resource hosted at the RS, the		To determine the AS in charge of a resource hosted at the RS, C MAY
	client C MAY send an initial Unauthorized Resource Request message to		send an initial Unauthorized Resource Request message to the RS. The
	the RS. The RS then denies the request and sends the address of its		RS then denies the request and sends an AS information message
	AS back to the client C as specified in section 5.1.2 of draft-ietf-		containing the address of its AS back to the client as specified in
	ace-oauth-authz [2].		Section 5.1.2 of draft-ietf-ace-oauth-authz [5].
	Once the client C knows the authorization server's address, it can
	send an Access Token request to the token endpoint at the AS as
	specified in [I-D.ietf-ace-oauth-authz]. As the Access Token request
	as well as the response may contain confidential data, the
	communication between the client and the authorization server MUST be
	confidentiality-protected and ensure authenticity. How the mutual
	authentication between the client and the authorization server is
	achieved is out of scope for this document; the client may have been
	configured with a public key of the authorization server and have
	been registered at the AS via the OAuth client registration mechanism
	as outlined in section 5.3 of draft-ietf-ace-oauth-authz [3].
	If C wants to use the CoAP RawPublicKey mode as described in
	Section 9 of RFC 7252 [4] it MUST provide a key or key identifier
	within a "cnf" object in the token request. If the authorization
	server AS decides that the request is to be authorized it generates
	an access token response for the client C containing a "profile"
	parameter with the value "coap_dtls" to indicate that this profile
	MUST be used for communication between the client C and the resource
	server.
	For RPK mode, the authorization server also adds a "rs_cnf" parameter
	containing information about the public that is used by the resource
	server (see Section 3).
	For PSK mode, the authorization server adds a "cnf" parameter		Once the client knows the authorization server's address, it can send
	containing information about the shared secret that C can use to		an access token request to the token endpoint at the AS as specified
	setup a DTLS session with the resource server (see Section 4).		in I-D.ietf-ace-oauth-authz [6]. As the access token request as well
			as the response may contain confidential data, the communication
			between the client and the authorization server MUST be
			confidentiality-protected and ensure authenticity. C may have been
			registered at the AS via the OAuth 2.0 client registration mechanism
			as outlined in Section 5.3 of draft-ietf-ace-oauth-authz [7].
	The Access Token returned by the authorization server then can be		The access token returned by the authorization server can then be
	used by the client to establish a new DTLS session with the resource		used by the client to establish a new DTLS session with the resource
	server. When the client intends to use asymmetric cryptography in		server. When the client intends to use asymmetric cryptography in
	the DTLS handshake with the resource server, the client MUST upload		the DTLS handshake with the resource server, the client MUST upload
	the Access Token to the authz-info resource on the resource server		the access token to the authz-info resource, i.e. the authz-info
	before starting the DTLS handshake, as described in section 5.8.1 of		endpoint, on the resource server before starting the DTLS handshake,
	draft-ietf-ace-oauth-authz [5]. If only symmetric cryptography is		as described in Section 5.8.1 of draft-ietf-ace-oauth-authz [8]. If
	used between the client and the resource server, the Access Token MAY		only symmetric cryptography is used between the client and the
	instead be transferred in the DTLS ClientKeyExchange message (see		resource server, the access token MAY instead be transferred in the
	Section 4.1).		DTLS ClientKeyExchange message (see Section 3.3.1).
	Figure 2 depicts the common protocol flow for the DTLS profile after		Figure 2 depicts the common protocol flow for the DTLS profile after
	the client C has retrieved the Access Token from the authorization		the client C has retrieved the access token from the authorization
	server AS.		server AS.
	C RS AS		C RS AS
	| [--- Access Token ------>] | |		| [--- Access Token ------>] | |
	| | |		| | |
	| <== DTLS channel setup ==> | |		| <== DTLS channel setup ==> | |
	| | |		| | |
	| == Authorized Request ===> | |		| == Authorized Request ===> | |
	| | |		| | |
	| <=== Protected Resource == | |		| <=== Protected Resource == | |
	Figure 2: Protocol overview		Figure 2: Protocol overview
	The following sections specify how CoAP is used to interchange		3. Protocol Flow
	access-related data between the resource server and the authorization
	server so that the authorization server can provide the client and
	the resource server with sufficient information to establish a secure
	channel, and convey authorization information specific for this
	communication relationship to the resource server.
	Depending on the desired CoAP security mode, the Client-to-AS
	request, AS-to-Client response and DTLS session establishment carry
	slightly different information. Section 3 addresses the use of raw
	public keys while Section 4 defines how pre-shared keys are used in
	this profile.
	2.1. Resource Access
	Once a DTLS channel has been established as described in Section 3
	and Section 4, respectively, the client is authorized to access
	resources covered by the Access Token it has uploaded to the authz-
	info resource hosted by the resource server.
	On the resource server side, successful establishment of the DTLS
	channel binds the client to the access token, functioning as a proof-
	of-possession associated key. Any request that the resource server
	receives on this channel MUST be checked against these authorization
	rules that are associated with the identity of the client. Incoming
	CoAP requests that are not authorized with respect to any Access
	Token that is associated with the client MUST be rejected by the
	resource server with 4.01 response as described in Section 5.1.1 of
	draft-ietf-ace-oauth-authz [6].
	Note: The identity of the client is determined by the authentication
	process
	during the DTLS handshake. In the asymmetric case, the public key
	will define the client's identity, while in the PSK case, the
	client's identity is defined by the shared secret generated by the
	authorization server for this communication.
	The resource server SHOULD treat an incoming CoAP request as
	authorized if the following holds:
	1. The message was received on a secure channel that has been
	established using the procedure defined in this document.
	2. The authorization information tied to the sending peer is valid.
	3. The request is destined for the resource server.
	4. The resource URI specified in the request is covered by the
	authorization information.
	5. The request method is an authorized action on the resource with
	respect to the authorization information.
	Incoming CoAP requests received on a secure DTLS channel MUST be
	rejected according to [Section 5.1.1 of draft-ietf-ace-oauth-
	authz](https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
	13#section-5.1.1
	1. with response code 4.03 (Forbidden) when the resource URI
	specified in the request is not covered by the authorization
	information, and
	2. with response code 4.05 (Method Not Allowed) when the resource
	URI specified in the request covered by the authorization
	information but not the requested action.
	The client cannot always know a priori if an Authorized Resource
	Request will succeed. If the client repeatedly gets error responses
	containing AS Information (cf. Section 5.1.1 of draft-ietf-ace-
	oauth-authz [7] as response to its requests, it SHOULD request a new
	Access Token from the authorization server in order to continue
	communication with the resource server.
	2.2. Dynamic Update of Authorization Information
	The client can update the authorization information stored at the
	resource server at any time without changing an established DTLS
	session. To do so, the Client requests from the authorization server
	a new Access Token for the intended action on the respective resource
	and uploads this Access Token to the authz-info resource on the
	resource server.
	Figure 3 depicts the message flow where the client C requests a new
	Access Token after a security association between the client and the
	resource server RS has been established using this protocol. The
	token request MUST specify the key identifier of the existing DTLS
	channel between the client and the resource server in the "kid"
	parameter of the Client-to-AS request. The authorization server MUST
	verify that the specified "kid" denotes a valid verifier for a proof-
	of-possession ticket that has previously been issued to the
	requesting client. Otherwise, the Client-to-AS request MUST be
	declined with a the error code "unsupported_pop_key" as defined in
	Section 5.6.3 of draft-ietf-ace-oauth-authz [8].
	When the authorization server issues a new access token to update
	existing authorization information it MUST include the specified
	"kid" parameter in this access token. A resource server MUST
	associate the updated authorization information with any existing
	DTLS session that is identified by this key identifier.
	Note: By associating the access tokens with the identifier of an
	existing DTLS session, the authorization information can be
	updated without changing the cryptographic keys for the DTLS
	communication between the client and the resource server, i.e. an
	existing session can be used with updated permissions.
	C RS AS
	| <===== DTLS channel =====> | |
	| + Access Token | |
	| | |
	| --- Token Request ----------------------------> |
	| | |
	| <---------------------------- New Access Token - |
	| + RS Information |
	| | |
	| --- Update /authz-info --> | |
	| New Access Token | |
	| | |
	| == Authorized Request ===> | |
	| | |
	| <=== Protected Resource == | |
	Figure 3: Overview of Dynamic Update Operation
	2.3. Token Expiration
	DTLS sessions that have been established in accordance with this
	profile are always tied to a specific set of access tokens. As these
	tokens may become invalid at any time (either because the token has
	expired or the responsible authorization server has revoked the
	token), the session may become useless at some point. A resource
	server therefore may decide to terminate existing DTLS sessions after
	the last valid access token for this session has been deleted.
	As specified in section 5.8.3 of draft-ietf-ace-oauth-authz [9], the		The following sections specify how CoAP is used to interchange
	resource server MUST notify the client with an error response with		access-related data between the resource server, the client and the
	code 4.01 (Unauthorized) for any long running request before		authorization server so that the authorization server can provide the
	terminating the session.		client and the resource server with sufficient information to
			establish a secure channel, and convey authorization information
			specific for this communication relationship to the resource server.
	The resource server MAY also keep the session alive for some time and		Section 3.1 describes how the communication between C and AS must be
	respond to incoming requests with a 4.01 (Unauthorized) error message		secured. Depending on the used CoAP security mode (see also
	including AS Information to signal that the client needs to upload a		Section 9 of RFC 7252 [9]), the Client-to-AS request, AS-to-Client
	new access token before it can continue using this DTLS session. The		response and DTLS session establishment carry slightly different
	AS Information is created as specified in section 5.1.2 of draft-		information. Section 3.2 addresses the use of raw public keys while
	ietf-ace-oauth-authz [10]. The resource server SHOULD add a "kid"		Section 3.3 defines how pre-shared keys are used in this profile.
	parameter to the AS Information denoting the identifier of the key
	that it uses internally for this DTLS session. The client then
	includes this "kid" parameter in a Client-to-AS request used to
	retrieve a new access token to be used with this DTLS session. In
	case the key identifier is already known by the client (e.g. because
	it was included in the RS Information in an AS-to-Client response),
	the "kid" parameter MAY be elided from the AS Information.
	Table 1 updates Figure 2 in section 5.1.2 of draft-ietf-ace-oauth-		3.1. Communication between C and AS
	authz [11] with the new "kid" parameter in accordance with [RFC8152].
	+----------------+----------+-----------------+		To retrieve an access token for the resource that the client wants to
	| Parameter name | CBOR Key | Major Type |		access, the client requests an access token from the authorization
	+----------------+----------+-----------------+		server. Before C can request the access token, C and AS must
	| kid | 4 | 2 (byte string) |		establish a secure communication channel. C must securely have
	+----------------+----------+-----------------+		obtained keying material to communicate with AS, and C must securely
			have received authorization information intended for C that states
			that AS is authorized to provide keying material concerning RS to C.
			Also, AS must securely have obtained keying material for C, and
			obtained authorization rules approved by the resource owner (RO)
			concerning C and RS that relate to this keying material. C and AS
			must use their respective keying material for all exchanged messages.
			How the security association between C and AS is established is not
			part of this document. C and AS MUST ensure the confidentiality,
			integrity and authenticity of all exchanged messages.
	Table 1: Updated AS Information parameters		If C is constrained, C and AS should use DTLS to communicate with
			each other. But C and AS may also use other means to secure their
			communication, e.g., TLS. The used security protocol must provide
			confidentiality, integrity and authenticity, and enable the client to
			determine if it is the intended recipient of a message, e.g., by
			using an AEAD mechanism. C must also be able to determine if a
			response from AS belongs to a certain request. Additionally, the
			protocol must offer replay protection.
	3. RawPublicKey Mode		3.2. RawPublicKey Mode
	To retrieve an access token for the resource that the client wants to		After C and AS mutually authenticated each other and validated each
	access, the client requests an Access Token from the authorization		other's authorization, C sends a token request to AS's token
	server. The client MUST add a "cnf" object carrying either its raw		endpoint. The client MUST add a "cnf" object carrying either its raw
	public key or a unique identifier for a public key that it has		public key or a unique identifier for a public key that it has
	previously made known to the authorization server. To prove that the		previously made known to the authorization server. To prove that the
	client is in possession of this key, it MUST use the same public key		client is in possession of this key, C MUST use the same keying
	as in certificate message that is used to establish the DTLS session		material that it uses to secure the communication with AS, e.g., the
	with the authorization server.		DTLS session.
	An example Access Token request from the client to the resource		An example access token request from the client to the AS is depicted
	server is depicted in Figure 4.		in Figure 3.
	POST coaps://as.example.com/token		POST coaps://as.example.com/token
	Content-Format: application/cbor		Content-Format: application/ace+cbor
	{		{
	grant_type: client_credentials,		grant_type: client_credentials,
	aud: "tempSensor4711",		req_aud: "tempSensor4711",
	cnf: {		req_cnf: {
	COSE_Key: {		COSE_Key: {
	kty: EC2,		kty: EC2,
	crv: P-256,		crv: P-256,
	x: h'TODOX',		x: h'e866c35f4c3c81bb96a1...',
	y: h'TODOY'		y: h'2e25556be097c8778a20...'
	}		}
	}		}
	}		}
	Figure 4: Access Token Request Example for RPK Mode		Figure 3: Access Token Request Example for RPK Mode
	The example shows an Access Token request for the resource identified		The example shows an access token request for the resource identified
	by the audience string "tempSensor4711" on the authorization server		by the string "tempSensor4711" on the authorization server using a
	using a raw public key.		raw public key.
	When the authorization server authorizes a request, it will return an		AS MUST check if the client that it communicates with is associated
	Access Token and a "cnf" object in the AS-to-Client response. Before		with the RPK in the cnf object before issuing an access token to it.
	the client initiates the DTLS handshake with the resource server, it		If AS determines that the request is to be authorized according to
	MUST send a "POST" request containing the new Access Token to the		the respective authorization rules, it generates an access token
	authz-info resource hosted by the resource server. If this operation		response for C. The response SHOULD contain a "profile" parameter
	yields a positive response, the client SHOULD proceed to establish a		with the value "coap_dtls" to indicate that this profile must be used
	new DTLS channel with the resource server. To use raw public key		for communication between the client C and the resource server. The
	mode, the client MUST pass the same public key that was used for		response also contains an access token and an "rs_cnf" parameter
	constructing the Access Token with the SubjectPublicKeyInfo structure		containing information about the public key that is used by the
	in the DTLS handshake as specified in [RFC7250].		resource server. AS MUST ascertain that the RPK specified in
			"rs_cnf" belongs to the resource server that C wants to communicate
			with. AS MUST protect the integrity of the token. If the access
			token contains confidential data, AS MUST also protect the
			confidentiality of the access token.
			C MUST ascertain that the access token response belongs to a certain
			previously sent access token request, as the request may specify the
			resource server with which C wants to communicate.
			3.2.1. DTLS Channel Setup Between C and RS
			Before the client initiates the DTLS handshake with the resource
			server, C MUST send a "POST" request containing the new access token
			to the authz-info resource hosted by the resource server. If this
			operation yields a positive response, the client SHOULD proceed to
			establish a new DTLS channel with the resource server. To use the
			RawPublicKey mode, the client MUST specify the public key that AS
			defined in the "cnf" field of the access token response in the
			SubjectPublicKeyInfo structure in the DTLS handshake as specified in
			RFC 7250 [10].
	An implementation that supports the RPK mode of this profile MUST at		An implementation that supports the RPK mode of this profile MUST at
	least support the ciphersuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8		least support the ciphersuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8
	[RFC7251] with the ed25519 curve (cf. [RFC8032], [RFC8422]).		[RFC7251] with the ed25519 curve (cf. [RFC8032], [RFC8422]).
	Note: According to [RFC7252], CoAP implementations MUST support the		Note: According to RFC 7252 [11], CoAP implementations MUST support
	ciphersuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 [RFC7251] and the		the ciphersuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 [RFC7251] and
	NIST P-256 curve. As discussed in [RFC7748], new ECC curves have		the NIST P-256 curve. As discussed in RFC 7748 [12], new ECC
	been defined recently that are considered superior to the so-		curves have been defined recently that are considered superior to
	called NIST curves. The curve that is mandatory to implement in		the so-called NIST curves. The curve that is mandatory to
	this specification is said to be efficient and less dangerous		implement in this specification is said to be efficient and less
	regarding implementation errors than the secp256r1 curve mandated		dangerous regarding implementation errors than the secp256r1 curve
	in [RFC7252].		mandated in RFC 7252 [13].
	The Access Token is constructed by the authorization server such that		RS MUST check if the access token is still valid, if RS is the
	the resource server can associate the Access Token with the Client's		intended destination, i.e., the audience, of the token, and if the
	public key. If CBOR web tokens [RFC8392] are used as recommended in		token was issued by an authorized AS. The access token is
	[I-D.ietf-ace-oauth-authz], the authorization server MUST include a		constructed by the authorization server such that the resource server
	"COSE_Key" object in the "cnf" claim of the Access Token. This		can associate the access token with the Client's public key. The
	"COSE_Key" object MAY contain a reference to a key for the client		"cnf" claim MUST contain either C's RPK or, if the key is already
	that is already known by the resource server (e.g., from previous		known by the resource server (e.g., from previous communication), a
	communication). If the authorization server has no certain knowledge		reference to this key. If the authorization server has no certain
	that the Client's key is already known to the resource server, the		knowledge that the Client's key is already known to the resource
	Client's public key MUST be included in the Access Token's "cnf"		server, the Client's public key MUST be included in the access
	parameter.		token's "cnf" parameter. If CBOR web tokens [RFC8392] are used as
			recommended in I-D.ietf-ace-oauth-authz [14], unencrypted keys MUST
			be specified using a "COSE_Key" object, encrypted keys with a
			"COSE_Encrypt0" structure and references to the key as "key_id"
			parameters in a CBOR map. RS MUST use the keying material in the
			handshake that AS specified in the rs_cnf parameter in the access
			token. Thus, the handshake only finishes if C and RS are able to use
			their respective keying material.
	4. PreSharedKey Mode		3.3. PreSharedKey Mode
	To retrieve an access token for the resource that the client wants to		To retrieve an access token for the resource that the client wants to
	access, the client MAY include a "cnf" object carrying an identifier		access, the client MAY include a "cnf" object carrying an identifier
	for a symmetric key in its Access Token request to the authorization		for a symmetric key in its access token request to the authorization
	server. This identifier can be used by the authorization server to		server. This identifier can be used by the authorization server to
	determine the shared secret to construct the proof-of-possession		determine the shared secret to construct the proof-of-possession
	token and therefore MUST specify a symmetric key that was previously		token. AS MUST check if the identifier refers to a symmetric key
	generated by the authorization server as a shared secret for the		that was previously generated by AS as a shared secret for the
	communication between the client and the resource server.		communication between this client and the resource server.
	Depending on the requested token type and algorithm in the Access		The authorization server MUST determine the authorization rules for
	Token request, the authorization server adds RS Information to the		the C it communicates with as defined by RO and generate the access
	response that provides the client with sufficient information to		token accordingly. If the authorization server authorizes the
	setup a DTLS channel with the resource server. For symmetric proof-		client, it returns an AS-to-Client response. If the profile
	of-possession keys (c.f. [I-D.ietf-ace-oauth-authz]), the client		parameter is present, it is set to "coap_dtls". AS MUST ascertain
	must ensure that the Access Token request is sent over a secure		that the access token is generated for the resource server that C
	channel that guarantees authentication, message integrity and		wants to communicate with. Also, AS MUST protect the integrity of
	confidentiality.		the access token. If the token contains confidential data such as
			the symmetric key, the confidentiality of the token MUST also be
			protected. Depending on the requested token type and algorithm in
			the access token request, the authorization server adds access
			Information to the response that provides the client with sufficient
			information to setup a DTLS channel with the resource server. AS
			adds a "cnf" parameter to the access information carrying a
			"COSE_Key" object that informs the client about the symmetric key
			that is to be used between C and the resource server.
	When the authorization server authorizes the client it returns an AS-		An example access token response is illustrated in Figure 4. In this
	to-Client response with the profile parameter set to "coap_dtls" and		example, the authorization server returns a 2.01 response containing
	a "cnf" parameter carrying a "COSE_Key" object that contains the		a new access token and information for the client, including the
	symmetric key to be used between the client and the resource server		symmetric key in the cnf claim. The information is transferred as a
	as illustrated in Figure 5.		CBOR data structure as specified in I-D.ietf-ace-oauth-authz [15].
	2.01 Created		2.01 Created
	Content-Format: application/cbor		Content-Format: application/ace+cbor
	Location-Path: /token/asdjbaskd		Max-Age: 86400
	{		{
	access_token: h'd08343a10...		access_token: h'd08343a10...
	(remainder of CWT omitted for brevity)		(remainder of CWT omitted for brevity)
	token_type: pop,		token_type: pop,
	alg: HS256,		alg: HS256,
	expires_in: 86400,		expires_in: 86400,
	profile: coap_dtls,		profile: coap_dtls,
	cnf: {		cnf: {
	COSE_Key: {		COSE_Key: {
	kty: symmetric,		kty: symmetric,
	k: h'73657373696f6e6b6579'		k: h'73657373696f6e6b6579'
	}		}
	}		}
	}		}
	Figure 5: Example Access Token response		Figure 4: Example Access Token Response
	In this example, the authorization server returns a 2.01 response		The access token also comprises a "cnf" claim. This claim usually
	containing a new Access Token. The information is transferred as a		contains a "COSE_Key" object that carries either the symmetric key
	CBOR data structure as specified in [I-D.ietf-ace-oauth-authz].		itself or or a key identifier that can be used by the resource server
			to determine the shared secret. If the access token carries a
			symmetric key, the access token MUST be encrypted using a
			"COSE_Encrypt0" structure. The AS MUST use the keying material
			shared with the RS to encrypt the token.
			Instead of providing the keying material, the AS MAY include a key
			derivation function and a salt in the access token that enables the
			resource server to calculate the keying material for the
			communication with C from the access token. In this case, the token
			contains a "cnf" structure that specifies the key derivation
			algorithm and the salt that the AS has used to construct the shared
			key. AS and RS MUST use their shared keying material for the key
			derivation, and the key derivation MUST follow Section 11 of RFC 8152
			[16] with parameters as specified here. The KDF specified in the
			"alg" parameter SHOULD be HKDF-SHA-256. The salt picked by the AS
			must be uniformly random and is carried in the "salt" parameter.
			The fields in the context information "COSE_KDF_Context"
			(Section 11.2 of RFC 8152 [17]) MUST have the following values:
			o AlgorithmID = "ACE-CoAP-DTLS-salt"
			o PartyUInfo = PartyVInfo = ( null, null, null )
			o keyDataLength is a uint equal the length of the key shared between
			AS and RS in bits
			o protected MUST be a zero length bstr
			o other is a zero length bstr
			o SuppPrivInfo is omitted
			An example "cnf" structure specifying HMAC-based key derivation of a
			symmetric key with SHA-256 as pseudo-random function and a random
			salt value is provided in Figure 5.
			cnf : {
			kty : symmetric,
			alg : HKDF-SHA-256,
			salt : h'eIiOFCa9lObw'
			}
			Figure 5: Key Derivation Specification in an Access Token
	A response that declines any operation on the requested resource is		A response that declines any operation on the requested resource is
	constructed according to Section 5.2 of RFC 6749 [12], (cf.		constructed according to Section 5.2 of RFC 6749 [18], (cf.
	Section 5.7.3 of [I-D.ietf-ace-oauth-authz]).		Section 5.7.3. of draft-ietf-ace-oauth-authz [19]).
	4.00 Bad Request		4.00 Bad Request
	Content-Format: application/cbor		Content-Format: application/ace+cbor
	{		{
	error: invalid_request		error: invalid_request
	}		}
	Figure 6: Example Access Token response with reject		Figure 6: Example Access Token Response With Reject
	4.1. DTLS Channel Setup Between C and RS		3.3.1. DTLS Channel Setup Between C and RS
	When a client receives an Access Token from an authorization server,		When a client receives an access token response from an authorization
	it checks if the payload contains an "access_token" parameter and a		server, C MUST ascertain that the access token response belongs to a
	"cnf" parameter. With this information the client can initiate		certain previously sent access token request, as the request may
	establishment of a new DTLS channel with a resource server. To use		specify the resource server with which C wants to communicate.
	DTLS with pre-shared keys, the client follows the PSK key exchange
	algorithm specified in Section 2 of [RFC4279] using the key conveyed		C checks if the payload of the access token response contains an
	in the "cnf" parameter of the AS response as PSK when constructing		"access_token" parameter and a "cnf" parameter. With this
	the premaster secret.		information the client can initiate the establishment of a new DTLS
			channel with a resource server. To use DTLS with pre-shared keys,
			the client follows the PSK key exchange algorithm specified in
			Section 2 of RFC 4279 [20] using the key conveyed in the "cnf"
			parameter of the AS response as PSK when constructing the premaster
			secret.
	In PreSharedKey mode, the knowledge of the shared secret by the		In PreSharedKey mode, the knowledge of the shared secret by the
	client and the resource server is used for mutual authentication		client and the resource server is used for mutual authentication
	between both peers. Therefore, the resource server must be able to		between both peers. Therefore, the resource server must be able to
	determine the shared secret from the Access Token. Following the		determine the shared secret from the access token. Following the
	general ACE authorization framework, the client can upload the Access		general ACE authorization framework, the client can upload the access
	Token to the resource server's authz-info resource before starting		token to the resource server's authz-info resource before starting
	the DTLS handshake. Alternatively, the client MAY provide the most		the DTLS handshake. Alternatively, the client MAY provide the most
	recent Access Token in the "psk_identity" field of the		recent access token in the "psk_identity" field of the
	ClientKeyExchange message. To do so, the client MUST treat the		ClientKeyExchange message. To do so, the client MUST treat the
	contents of the "access_token" field from the AS-to-Client response		contents of the "access_token" field from the AS-to-Client response
	as opaque data and not perform any re-coding.		as opaque data and not perform any re-coding.
	Note: As stated in section 4.2 of [RFC7925], the PSK identity should		Note: As stated in Section 4.2 of RFC 7925 [21], the PSK identity
	be treated as binary data in the Internet of Things space and not		should be treated as binary data in the Internet of Things space
	assumed to have a human-readable form of any sort.		and not assumed to have a human-readable form of any sort.
	If a resource server receives a ClientKeyExchange message that		If a resource server receives a ClientKeyExchange message that
	contains a "psk_identity" with a length greater zero, it uses the		contains a "psk_identity" with a length greater zero, it uses the
	contents as index for its key store (i.e., treat the contents as key		contents as index for its key store (i.e., treat the contents as key
	identifier). The resource server MUST check if it has one or more		identifier). The resource server MUST check if it has one or more
	Access Tokens that are associated with the specified key. If no		access tokens that are associated with the specified key.
	valid Access Token is available for this key, the DTLS session setup
	is terminated with an "illegal_parameter" DTLS alert message.
	If no key with a matching identifier is found the resource server the		If no key with a matching identifier is found, the resource server
	resource server MAY process the decoded contents of the		MAY process the contents of the "psk_identity" field as access token
	"psk_identity" field as access token that is stored with the		that is stored with the authorization information endpoint, before
	authorization information endpoint before continuing the DTLS		continuing the DTLS handshake. If the contents of the "psk_identity"
	handshake. If the decoded contents of the "psk_identity" do not		do not yield a valid access token for the requesting client, the DTLS
	yield a valid access token for the requesting client, the DTLS
	session setup is terminated with an "illegal_parameter" DTLS alert		session setup is terminated with an "illegal_parameter" DTLS alert
	message.		message.
	Note1: As a resource server cannot provide a client with a meaningful		Note1: As a resource server cannot provide a client with a
	PSK identity hint in		meaningful PSK identity hint in response to the client's
	response to the client's ClientHello message, the resource server		ClientHello message, the resource server SHOULD NOT send a
	SHOULD NOT send a ServerKeyExchange message.		ServerKeyExchange message.
	Note2: According to [RFC7252], CoAP implementations MUST support the		Note2: According to RFC 7252 [22], CoAP implementations MUST support
	ciphersuite TLS_PSK_WITH_AES_128_CCM_8 [RFC6655]. A client is		the ciphersuite TLS_PSK_WITH_AES_128_CCM_8 [RFC6655]. A client is
	therefore expected to offer at least this ciphersuite to the		therefore expected to offer at least this ciphersuite to the
	resource server.		resource server.
	This specification assumes that the Access Token is a PoP token as		When RS receives an access token, RS MUST check if the access token
	described in [I-D.ietf-ace-oauth-authz] unless specifically stated		is still valid, if RS is the intended destination, i.e., the audience
	otherwise. Therefore, the Access Token is bound to a symmetric PoP		of the token, and if the token was issued by an authorized AS. This
			specification assumes that the access token is a PoP token as
			described in I-D.ietf-ace-oauth-authz [23] unless specifically stated
			otherwise. Therefore, the access token is bound to a symmetric PoP
	key that is used as shared secret between the client and the resource		key that is used as shared secret between the client and the resource
	server.		server.
	While the client can retrieve the shared secret from the contents of		While the client can retrieve the shared secret from the contents of
	the "cnf" parameter in the AS-to-Client response, the resource server		the "cnf" parameter in the AS-to-Client response, the resource server
	uses the information contained in the "cnf" claim of the Access Token		uses the information contained in the "cnf" claim of the access token
	to determine the actual secret when no explicit "kid" was provided in		to determine the actual secret when no explicit "kid" was provided in
	the "psk_identity" field. Usually, this is done by including a		the "psk_identity" field. If key derivation is used, the RS uses the
	"COSE_Key" object carrying either a key that has been encrypted with		"COSE_KDF_Context" information as described above.
	a shared secret between the authorization server and the resource
	server, or a key identifier that can be used by the resource server
	to lookup the shared secret.
	Instead of the "COSE_Key" object, the authorization server MAY		3.4. Resource Access
	include a "COSE_Encrypt" structure to enable the resource server to
	calculate the shared key from the Access Token. The "COSE_Encrypt"
	structure MUST use the _Direct Key with KDF_ method as described in
	Section 12.1.2 of RFC 8152 [13]. The authorization server MUST
	include a Context information structure carrying a PartyU "nonce"
	parameter carrying the nonce that has been used by the authorization
	server to construct the shared key.
	This specification mandates that at least the key derivation		Once a DTLS channel has been established as described in Section 3.2
	algorithm "HKDF SHA-256" as defined in [RFC8152] MUST be supported.		and Section 3.3, respectively, the client is authorized to access
	This key derivation function is the default when no "alg" field is		resources covered by the access token it has uploaded to the authz-
	included in the "COSE_Encrypt" structure for the resource server.		info resource hosted by the resource server.
	4.2. Updating Authorization Information		With the successful establishment of the DTLS channel, C and RS have
			proven that they can use their respective keying material. An access
			token that is bound to the client's keying material is associated
			with the channel. Any request that the resource server receives on
			this channel MUST be checked against these authorization rules. RS
			MUST check for every request if the access token is still valid.
			Incoming CoAP requests that are not authorized with respect to any
			access token that is associated with the client MUST be rejected by
			the resource server with 4.01 response as described in Section 5.1.1
			of draft-ietf-ace-oauth-authz [24].
	Usually, the authorization information that the resource server keeps		The resource server SHOULD treat an incoming CoAP request as
	for a client is updated by uploading a new Access Token as described		authorized if the following holds:
	in Section 2.2.
	The Client MAY also perform a new DTLS handshake according to		1. The message was received on a secure channel that has been
	Section 4.1 that replaces the existing DTLS session. After		established using the procedure defined in this document.
	successful completion of the DTLS handshake the resource server
	updates the existing authorization information for the client
	according to the new Access Token.
	5. Security Considerations		2. The authorization information tied to the sending client is
			valid.
			3. The request is destined for the resource server.
			4. The resource URI specified in the request is covered by the
			authorization information.
			5. The request method is an authorized action on the resource with
			respect to the authorization information.
			Incoming CoAP requests received on a secure DTLS channel that are not
			thus authorized MUST be rejected according to Section 5.8.2 of draft-
			ietf-ace-oauth-authz [25]
			1. with response code 4.03 (Forbidden) when the resource URI
			specified in the request is not covered by the authorization
			information, and
			2. with response code 4.05 (Method Not Allowed) when the resource
			URI specified in the request covered by the authorization
			information but not the requested action.
			The client cannot always know a priori if an Authorized Resource
			Request will succeed. If the client repeatedly gets error responses
			containing AS Information (cf. Section 5.1.2 of draft-ietf-ace-
			oauth-authz [26]) as response to its requests, it SHOULD request a
			new access token from the authorization server in order to continue
			communication with the resource server.
			4. Dynamic Update of Authorization Information
			The client can update the authorization information stored at the
			resource server at any time without changing an established DTLS
			session. To do so, the Client requests a new access token from the
			authorization server for the intended action on the respective
			resource and uploads this access token to the authz-info resource on
			the resource server.
			Figure 7 depicts the message flow where the C requests a new access
			token after a security association between the client and the
			resource server has been established using this protocol. If the
			client wants to update the authorization information, the token
			request MUST specify the key identifier of the existing DTLS channel
			between the client and the resource server in the "kid" parameter of
			the Client-to-AS request. The authorization server MUST verify that
			the specified "kid" denotes a valid verifier for a proof-of-
			possession token that has previously been issued to the requesting
			client. Otherwise, the Client-to-AS request MUST be declined with
			the error code "unsupported_pop_key" as defined in Section 5.6.3 of
			draft-ietf-ace-oauth-authz [27].
			When the authorization server issues a new access token to update
			existing authorization information, it MUST include the specified
			"kid" parameter in this access token. A resource server MUST
			associate the updated authorization information with any existing
			DTLS session that is identified by this key identifier.
			Note: By associating the access tokens with the identifier of an
			existing DTLS session, the authorization information can be
			updated without changing the cryptographic keys for the DTLS
			communication between the client and the resource server, i.e. an
			existing session can be used with updated permissions.
			C RS AS
			| <===== DTLS channel =====> | |
			| + Access Token | |
			| | |
			| --- Token Request ----------------------------> |
			| | |
			| <---------------------------- New Access Token - |
			| + Access Information |
			| | |
			| --- Update /authz-info --> | |
			| New Access Token | |
			| | |
			| == Authorized Request ===> | |
			| | |
			| <=== Protected Resource == | |
			Figure 7: Overview of Dynamic Update Operation
			5. Token Expiration
			DTLS sessions that have been established in accordance with this
			profile are always tied to a specific set of access tokens. As these
			tokens may become invalid at any time (either because the token has
			expired or the responsible authorization server has revoked the
			token), the session may become useless at some point. A resource
			server therefore MUST terminate existing DTLS sessions after the last
			valid access token for this session has been deleted.
			As specified in Section 5.8.3 of draft-ietf-ace-oauth-authz [28], the
			resource server MUST notify the client with an error response with
			code 4.01 (Unauthorized) for any long running request before
			terminating the session.
			Table 1 updates Figure 2 in Section 5.1.2 of draft-ietf-ace-oauth-
			authz [29] with the new "kid" parameter in accordance with [RFC8152].
			+----------------+----------+-----------------+
			| Parameter name | CBOR Key | Major Type |
			+----------------+----------+-----------------+
			| kid | 4 | 2 (byte string) |
			+----------------+----------+-----------------+
			Table 1: Updated AS Information parameters
			6. Security Considerations
	This document specifies a profile for the Authentication and		This document specifies a profile for the Authentication and
	Authorization for Constrained Environments (ACE) framework		Authorization for Constrained Environments (ACE) framework
	[I-D.ietf-ace-oauth-authz]. As it follows this framework's general		[I-D.ietf-ace-oauth-authz]. As it follows this framework's general
	approach, the general security and privacy considerations from		approach, the general security and privacy considerations from
	section 6 and section 7 also apply to this profile.		section 6 and section 7 also apply to this profile.
	Constrained devices that use DTLS [RFC6347] are inherently vulnerable		Constrained devices that use DTLS [RFC6347] are inherently vulnerable
	to Denial of Service (DoS) attacks as the handshake protocol requires		to Denial of Service (DoS) attacks as the handshake protocol requires
	creation of internal state within the device. This is specifically		creation of internal state within the device. This is specifically
	of concern where an adversary is able to intercept the initial cookie		of concern where an adversary is able to intercept the initial cookie
	exchange and interject forged messages with a valid cookie to		exchange and interject forged messages with a valid cookie to
	continue with the handshake.		continue with the handshake.
	[I-D.tiloca-tls-dos-handshake] specifies a TLS extension to prevent		[I-D.tiloca-tls-dos-handshake] specifies a TLS extension to prevent
	this type of attack which is applicable especially for constrained		this type of attack which is applicable especially for constrained
	environments where the authorization server can act as trust anchor.		environments where the authorization server can act as trust anchor.
	6. Privacy Considerations		The use of multiple access tokens for a single client increases the
			strain on the resource server as it must consider every access token
			and calculate the actual permissions of the client. Also, tokens may
			contradict each other which may lead the server to enforce wrong
			permissions. If one of the access tokens expires earlier than
			others, the resulting permissions may offer insufficient protection.
			Developers should avoid using multiple access tokens for a client.
			7. Privacy Considerations
	An unprotected response to an unauthorized request may disclose		An unprotected response to an unauthorized request may disclose
	information about the resource server and/or its existing		information about the resource server and/or its existing
	relationship with the client. It is advisable to include as little		relationship with the client. It is advisable to include as little
	information as possible in an unencrypted response. When a DTLS		information as possible in an unencrypted response. When a DTLS
	session between the client and the resource server already exists,		session between the client and the resource server already exists,
	more detailed information may be included with an error response to		more detailed information may be included with an error response to
	provide the client with sufficient information to react on that		provide the client with sufficient information to react on that
	particular error.		particular error.
			Also, unprotected requests to the resource server may reveal
			information about the client, e.g., which resources the client
			attempts to request or the data that the client wants to provide to
			the resource server. The client should not send confidential data in
			an unprotected request.
	Note that some information might still leak after DTLS session is		Note that some information might still leak after DTLS session is
	established, due to observable message sizes, the source, and the		established, due to observable message sizes, the source, and the
	destination addresses.		destination addresses.
	7. IANA Considerations		8. IANA Considerations
	The following registrations are done for the ACE OAuth Profile		The following registrations are done for the ACE OAuth Profile
	Registry following the procedure specified in		Registry following the procedure specified in
	[I-D.ietf-ace-oauth-authz].		[I-D.ietf-ace-oauth-authz].
	Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"		Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
	with the RFC number of this specification and delete this paragraph.		with the RFC number of this specification and delete this paragraph.
	Profile name: coap_dtls		Profile name: coap_dtls
	skipping to change at page 15, line 13 ¶		skipping to change at page 16, line 27 ¶
	authorization in a constrained environment by establishing a Datagram		authorization in a constrained environment by establishing a Datagram
	Transport Layer Security (DTLS) channel between resource-constrained		Transport Layer Security (DTLS) channel between resource-constrained
	nodes.		nodes.
	Profile ID: 1		Profile ID: 1
	Change Controller: IESG		Change Controller: IESG
	Reference: [RFC-XXXX]		Reference: [RFC-XXXX]
	8. References		9. References
	8.1. Normative References		9.1. Normative References
	[I-D.ietf-ace-oauth-authz]		[I-D.ietf-ace-oauth-authz]
	Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and		Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
	H. Tschofenig, "Authentication and Authorization for		H. Tschofenig, "Authentication and Authorization for
	Constrained Environments (ACE) using the OAuth 2.0		Constrained Environments (ACE) using the OAuth 2.0
	Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-13		Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-16
	(work in progress), July 2018.		(work in progress), October 2018.
	[I-D.tiloca-tls-dos-handshake]		[I-D.tiloca-tls-dos-handshake]
	Tiloca, M., Seitz, L., Hoeve, M., and O. Bergmann,		Tiloca, M., Seitz, L., Hoeve, M., and O. Bergmann,
	"Extension for protecting (D)TLS handshakes against Denial		"Extension for protecting (D)TLS handshakes against Denial
	of Service", draft-tiloca-tls-dos-handshake-02 (work in		of Service", draft-tiloca-tls-dos-handshake-02 (work in
	progress), March 2018.		progress), March 2018.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key		[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
	Ciphersuites for Transport Layer Security (TLS)",		Ciphersuites for Transport Layer Security (TLS)",
	RFC 4279, DOI 10.17487/RFC4279, December 2005,		RFC 4279, DOI 10.17487/RFC4279, December 2005,
	<https://www.rfc-editor.org/info/rfc4279>.		<https://www.rfc-editor.org/info/rfc4279>.
	[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
	"Transport Layer Security (TLS) Renegotiation Indication
	Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010,
	<https://www.rfc-editor.org/info/rfc5746>.
	[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer		[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
	Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,		Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
	January 2012, <https://www.rfc-editor.org/info/rfc6347>.		January 2012, <https://www.rfc-editor.org/info/rfc6347>.
	[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained		[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
	Application Protocol (CoAP)", RFC 7252,		Application Protocol (CoAP)", RFC 7252,
	DOI 10.17487/RFC7252, June 2014,		DOI 10.17487/RFC7252, June 2014,
	<https://www.rfc-editor.org/info/rfc7252>.		<https://www.rfc-editor.org/info/rfc7252>.
	[RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer		[RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer
	skipping to change at page 16, line 24 ¶		skipping to change at page 17, line 28 ¶
	<https://www.rfc-editor.org/info/rfc7925>.		<https://www.rfc-editor.org/info/rfc7925>.
	[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",		[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
	RFC 8152, DOI 10.17487/RFC8152, July 2017,		RFC 8152, DOI 10.17487/RFC8152, July 2017,
	<https://www.rfc-editor.org/info/rfc8152>.		<https://www.rfc-editor.org/info/rfc8152>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	8.2. Informative References		9.2. Informative References
	[RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for		[RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
	Transport Layer Security (TLS)", RFC 6655,		Transport Layer Security (TLS)", RFC 6655,
	DOI 10.17487/RFC6655, July 2012,		DOI 10.17487/RFC6655, July 2012,
	<https://www.rfc-editor.org/info/rfc6655>.		<https://www.rfc-editor.org/info/rfc6655>.
	[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,		[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
	Weiler, S., and T. Kivinen, "Using Raw Public Keys in		Weiler, S., and T. Kivinen, "Using Raw Public Keys in
	Transport Layer Security (TLS) and Datagram Transport		Transport Layer Security (TLS) and Datagram Transport
	Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,		Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
	skipping to change at page 17, line 15 ¶		skipping to change at page 18, line 20 ¶
	[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,		[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
	"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,		"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
	May 2018, <https://www.rfc-editor.org/info/rfc8392>.		May 2018, <https://www.rfc-editor.org/info/rfc8392>.
	[RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic		[RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
	Curve Cryptography (ECC) Cipher Suites for Transport Layer		Curve Cryptography (ECC) Cipher Suites for Transport Layer
	Security (TLS) Versions 1.2 and Earlier", RFC 8422,		Security (TLS) Versions 1.2 and Earlier", RFC 8422,
	DOI 10.17487/RFC8422, August 2018,		DOI 10.17487/RFC8422, August 2018,
	<https://www.rfc-editor.org/info/rfc8422>.		<https://www.rfc-editor.org/info/rfc8422>.
	8.3. URIs		9.3. URIs
	[1] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[1] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
	13#section-5.8.1		16#section-5.8.1
	[2] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[2] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz
	13#section-5.1.2
	[3] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[3] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz
	13#section-5.3
	[4] https://tools.ietf.org/html/rfc7252#section-9		[4] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz
	[5] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[5] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
	13#section-5.8.1		16#section-5.1.2
	[6] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[6] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz
	13#section-5.1.1
	[7] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[7] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
	13#section-5.1.1		16#section-5.3
	[8] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[8] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
	13#section-5.6.3		16#section-5.8.1
	[9] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[9] https://tools.ietf.org/html/rfc7252#section-9
	13#section-5.8.3
	[10] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[10] https://tools.ietf.org/html/rfc7250
	13#section-5.1.2
	[11] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-		[11] https://tools.ietf.org/html/rfc7252
	13#section-5.1.2
	[12] https://tools.ietf.org/html/rfc6749#section-5.2		[12] https://tools.ietf.org/html/rfc7748
	[13] https://tools.ietf.org/html/rfc8152#section-12.1.2		[13] https://tools.ietf.org/html/rfc7252
			[14] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz
			[15] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz
			[16] https://tools.ietf.org/html/rfc8152#section-11
			[17] https://tools.ietf.org/html/rfc8152#section-11.2
			[18] https://tools.ietf.org/html/rfc6749#section-5.2
			[19] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz#section-
			5.7.3
			[20] https://tools.ietf.org/html/rfc4279#section-2
			[21] https://tools.ietf.org/html/rfc7925#section-4.2
			[22] https://tools.ietf.org/html/rfc7252
			[23] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz
			[24] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
			16#section-5.1.1
			[25] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
			16#section-5.8.2
			[26] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
			16#section-5.1.2
			[27] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
			16#section-5.6.3
			[28] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
			16#section-5.8.3
			[29] https://tools.ietf.org/html/draft-ietf-ace-oauth-authz-
			16#section-5.1.2
	Authors' Addresses		Authors' Addresses
	Stefanie Gerdes		Stefanie Gerdes
	Universitaet Bremen TZI		Universitaet Bremen TZI
	Postfach 330440		Postfach 330440
	Bremen D-28359		Bremen D-28359
	Germany		Germany
	Phone: +49-421-218-63906		Phone: +49-421-218-63906
	skipping to change at page 18, line 35 ¶		skipping to change at page 20, line 23 ¶
	Carsten Bormann		Carsten Bormann
	Universitaet Bremen TZI		Universitaet Bremen TZI
	Postfach 330440		Postfach 330440
	Bremen D-28359		Bremen D-28359
	Germany		Germany
	Phone: +49-421-218-63921		Phone: +49-421-218-63921
	Email: cabo@tzi.org		Email: cabo@tzi.org
	Goeran Selander		Goeran Selander
	Ericsson		Ericsson AB
	Faroegatan 6
	Kista 164 80
	Sweden
	Email: goran.selander@ericsson.com		Email: goran.selander@ericsson.com
	Ludwig Seitz		Ludwig Seitz
	RISE SICS		RISE SICS
	Scheelevaegen 17		Scheelevaegen 17
	Lund 223 70		Lund 223 70
	Sweden		Sweden
	Email: ludwig.seitz@ri.se		Email: ludwig.seitz@ri.se
End of changes. 89 change blocks.
	430 lines changed or deleted		520 lines changed or added
This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/