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Versions: (draft-bradley-oauth-pop-key-distribution) 00 01 02 03 04 05 06 07

Network Working Group                                         J. Bradley
Internet-Draft                                             Ping Identity
Intended status: Standards Track                                 P. Hunt
Expires: April 26, 2019                               Oracle Corporation
                                                                M. Jones
                                                               Microsoft
                                                           H. Tschofenig
                                                                Arm Ltd.
                                                               M. Mihaly
                                                          NIIF Institute
                                                        October 23, 2018


   OAuth 2.0 Proof-of-Possession: Authorization Server to Client Key
                              Distribution
                draft-ietf-oauth-pop-key-distribution-04

Abstract

   RFC 6750 specified the bearer token concept for securing access to
   protected resources.  Bearer tokens need to be protected in transit
   as well as at rest.  When a client requests access to a protected
   resource it hands-over the bearer token to the resource server.

   The OAuth 2.0 Proof-of-Possession security concept extends bearer
   token security and requires the client to demonstrate possession of a
   key when accessing a protected resource.

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 https://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 April 26, 2019.







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Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Processing Instructions . . . . . . . . . . . . . . . . . . .   4
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Symmetric Key Transport . . . . . . . . . . . . . . . . .   5
       4.1.1.  Client-to-AS Request  . . . . . . . . . . . . . . . .   5
       4.1.2.  Client-to-AS Response . . . . . . . . . . . . . . . .   6
     4.2.  Asymmetric Key Transport  . . . . . . . . . . . . . . . .   9
       4.2.1.  Client-to-AS Request  . . . . . . . . . . . . . . . .   9
       4.2.2.  Client-to-AS Response . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  OAuth Access Token Types  . . . . . . . . . . . . . . . .  13
     6.2.  OAuth Parameters Registration . . . . . . . . . . . . . .  13
     6.3.  OAuth Extensions Error Registration . . . . . . . . . . .  13
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   The work on proof-of-possession tokens, an extended token security
   mechanisms for OAuth 2.0, is motivated in [21].  This document
   defines the ability for the client request and to obtain PoP tokens
   from the authorization server.  After successfully completing the
   exchange the client is in possession of a PoP token and the keying
   material bound to it.  Clients that access protected resources then
   need to demonstrate knowledge of the secret key that is bound to the
   PoP token.



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   To best describe the scope of this specification, the OAuth 2.0
   protocol exchange sequence is shown in Figure 1.  The extension
   defined in this document piggybacks on the message exchange marked
   with (C) and (D).  To demonstrate possession of the private/secret
   key to the resource server protocol mechanisms outside the scope of
   this document are used.

   +--------+                               +---------------+
   |        |--(A)- Authorization Request ->|   Resource    |
   |        |                               |     Owner     |
   |        |<-(B)-- Authorization Grant ---|               |
   |        |                               +---------------+
   |        |
   |        |                               +---------------+
   |        |--(C)-- Authorization Grant -->|               |
   | Client |       (resource, req_cnf)     | Authorization |
   |        |                               |     Server    |
   |        |<-(D)-- PoP Access Token ------|               |
   |        |       (rs_cnf, token_type)    +---------------+
   |        |
   |        |                               +---------------+
   |        |--(E)-- PoP Access Token ----->|               |
   |        |   (with proof of private key) |    Resource   |
   |        |                               |     Server    |
   |        |<-(F)--- Protected Resource ---|               |
   +--------+                               +---------------+

                Figure 1: Augmented OAuth 2.0 Protocol Flow

   In OAuth 2.0 [2] access tokens can be obtained via authorization
   grants and using refresh tokens.  The core OAuth specification
   defines four authorization grants, see Section 1.3 of [2], and [18]
   adds an assertion-based authorization grant to that list.  The token
   endpoint, which is described in Section 3.2 of [2], is used with
   every authorization grant except for the implicit grant type.  In the
   implicit grant type the access token is issued directly.

   This specification extends the functionality of the token endpoint,
   i.e., the protocol exchange between the client and the authorization
   server, to allow keying material to be bound to an access token.  Two
   types of keying material can be bound to an access token, namely
   symmetric keys and asymmetric keys.  Conveying symmetric keys from
   the authorization server to the client is described in Section 4.1
   and the procedure for dealing with asymmetric keys is described in
   Section 4.2.

   This document describes how the client requests and obtains a PoP
   access token from the authorization server for use with HTTPS-based



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   transport.  The use of alternative transports, such as Constrained
   Application Protocol (CoAP), is described in [23].

2.  Terminology

   The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
   'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in this
   specification are to be interpreted as described in [1].

   Session Key:

      In the context of this specification 'session key' refers to fresh
      and unique keying material established between the client and the
      resource server.  This session key has a lifetime that corresponds
      to the lifetime of the access token, is generated by the
      authorization server and bound to the access token.

   This document uses the following abbreviations:

   JWA:  JSON Web Algorithms[7]

   JWT:  JSON Web Token[9]

   JWS:  JSON Web Signature[6]

   JWK:  JSON Web Key[5]

   JWE:  JSON Web Encryption[8]

   CWT:  CBOR Web Token[13]

   COSE:  CBOR Object Signing and Encryption[14]

3.  Processing Instructions

      Step (0): As an initial step the client typically determines the
      resource server it wants to interact with.  This may, for example,
      happen as part of a discovery procedure or via manual
      configuration.

      Step (1): The client starts the OAuth 2.0 protocol interaction
      based on the selected grant type.

      Step (2): When the client interacts with the token endpoint to
      obtain an access token it MUST use the resource identicator
      defined in [15] when symmetric PoP tokens are used.  For
      asymmetric PoP tokens the use of resource indicators is optional
      but recommended.



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      Step (2): The authorization server parses the request from the
      server and determines the suitable response based on OAuth 2.0 and
      the PoP token credential procedures.

   Note that PoP access tokens may be encoded in a variety of ways:

   JWT  The access token may be encoded using the JSON Web Token (JWT)
      format [9].  The proof-of-possession token functionality is
      described in [10].  A JWT encoded PoP token MUST be protected
      against modification by either using a digital signature or a
      keyed message digest, as described in [6].  The JWT may also be
      encrypted using [8].

   CWT  [13] defines an alternative token format based on CBOR.  The
      proof-of-possession token functionality is defined in [12].  A CWT
      encoded PoP token MUST be protected against modification by either
      using a digital signature or a keyed message digest, as described
      in [12].

   If the access token is only a reference then a look-up by the
   resource server is needed, as described in the token introspection
   specification [22].

   Note that the OAuth 2.0 framework nor this specification does not
   mandate a specific PoP token format but using a standardized format
   will improve interoperability and will lead to better code re-use.

   Application layer interactions between the client and the resource
   server are beyond the scope of this document.

4.  Examples

   This section provides a number of examples.

4.1.  Symmetric Key Transport

4.1.1.  Client-to-AS Request

   The client starts with a request to the authorization server
   indicating that it is interested to obtain a token for
   https://www.example.com










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        POST /token HTTP/1.1
        Host: server.example.com
        Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
        Content-Type: application/x-www-form-urlencoded;charset=UTF-8

        grant_type=authorization_code
        &code=SplxlOBeZQQYbYS6WxSbIA
        &redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
        &resource=https://www.example.com


                Example Request to the Authorization Server

4.1.2.  Client-to-AS Response

   If the access token request has been successfully verified by the
   authorization server and the client is authorized to obtain a PoP
   token for the indicated resource server, the authorization server
   issues an access token and optionally a refresh token.

   Figure 2 shows a response containing a token and a "cnf" parameter
   with a symmetric proof-of-possession key both encoded in a JSON-based
   serialization format.  The "cnf" parameter contains the RFC 7517 [5]
   encoded key element.



























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     HTTP/1.1 200 OK
     Content-Type: application/json
     Cache-Control: no-store

     {
       "access_token":"SlAV32hkKG ...
        (remainder of JWT omitted for brevity;
        JWT contains JWK in the cnf claim)",
       "token_type":"pop",
       "expires_in":3600,
       "refresh_token":"8xLOxBtZp8",
       "cnf":{
         {"keys":
          [
            {"kty":"oct",
              "alg":"A128KW",
              "k":"GawgguFyGrWKav7AX4VKUg"
                    }
               ]
             }
           }
     }


   Figure 2: Example: Response from the Authorization Server (Symmetric
                                 Variant)

   Note that the cnf payload in Figure 2 is not encrypted at the
   application layer since Transport Layer Security is used between the
   AS and the client and the content of the cnf payload is consumed by
   the client itself.  Alternatively, a JWE could be used to encrypt the
   key distribution, as shown in Figure 3.



















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     {
       "access_token":"SlAV32hkKG ...
        (remainder of JWT omitted for brevity;
        JWT contains JWK in the cnf claim)",
       "token_type":"pop",
       "expires_in":3600,
       "refresh_token":"8xLOxBtZp8",
       "cnf":{
           "jwe":
             "eyJhbGciOiJSU0EtT0FFUCIsImVuYyI6IkExMjhDQkMtSFMyNTYifQ.
             (remainder of JWE omitted for brevity)"
           }
           }
     }


                Figure 3: Example: Encrypted Symmmetric Key

   The content of the 'access_token' in JWT format contains the 'cnf'
   (confirmation) claim.  The confirmation claim is defined in [10].
   The digital signature or the keyed message digest offering integrity
   protection is not shown in this example but has to be present in a
   real deployment to mitigate a number of security threats.

   The JWK in the key element of the response from the authorization
   server, as shown in Figure 2, contains the same session key as the
   JWK inside the access token, as shown in Figure 4.  It is, in this
   example, protected by TLS and transmitted from the authorization
   server to the client (for processing by the client).


      {
         "iss": "https://server.example.com",
         "sub": "24400320",
         "aud": "s6BhdRkqt3",
         "nonce": "n-0S6_WzA2Mj",
         "exp": 1311281970,
         "iat": 1311280970,
         "cnf":{
           "jwe":
             "eyJhbGciOiJSU0EtT0FFUCIsImVuYyI6IkExMjhDQkMtSFMyNTYifQ.
             (remainder of JWE omitted for brevity)"
           }
      }


               Figure 4: Example: Access Token in JWT Format




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   Note: When the JWK inside the access token contains a symmetric key
   it must be confidentiality protected using a JWE to maintain the
   security goals of the PoP architecture since content is meant for
   consumption by the selected resource server only.  The details are
   described in [21].

4.2.  Asymmetric Key Transport

4.2.1.  Client-to-AS Request

   This example illustrates the case where an asymmetric key shall be
   bound to an access token.  The client makes the following HTTPS
   request shown in Figure 5.  Extra line breaks are for display
   purposes only.


        POST /token HTTP/1.1
        Host: server.example.com
        Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
        Content-Type: application/x-www-form-urlencoded;charset=UTF-8

        grant_type=authorization_code
        &code=SplxlOBeZQQYbYS6WxSbIA
        &redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
        &token_type=pop
        &req_cnf=eyJhbGciOiJSU0ExXzUi ...
        (remainder of JWK omitted for brevity)

   Figure 5: Example Request to the Authorization Server (Asymmetric Key
                                 Variant)

   As shown in Figure 6 the content of the 'req_cnf' parameter contains
   the ECC public key the client would like to associate with the access
   token (in JSON format).


           "jwk":{
             "kty": "EC",
             "use": "sig",
             "crv": "P-256",
             "x": "18wHLeIgW9wVN6VD1Txgpqy2LszYkMf6J8njVAibvhM",
             "y": "-V4dS4UaLMgP_4fY4j8ir7cl1TXlFdAgcx55o7TkcSA"
            }

       Figure 6: Client Providing Public Key to Authorization Server






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4.2.2.  Client-to-AS Response

   If the access token request is valid and authorized, the
   authorization server issues an access token and optionally a refresh
   token.  The authorization server also places information about the
   public key used by the client into the access token to create the
   binding between the two.  The new token type "pop" is placed into the
   'token_type' parameter.

   An example of a successful response is shown in Figure 7.


        HTTP/1.1 200 OK
        Content-Type: application/json;charset=UTF-8
        Cache-Control: no-store
        Pragma: no-cache

        {
          "access_token":"2YotnFZFE....jr1zCsicMWpAA",
          "token_type":"pop",
          "expires_in":3600,
          "refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA"
        }

   Figure 7: Example: Response from the Authorization Server (Asymmetric
                                 Variant)

   The content of the 'access_token' field contains an encoded JWT, as
   shown in Figure 8.  The digital signature covering the access token
   offering authenticity and integrity protection is not shown below
   (but must be present).




















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       {
         "iss":"xas.example.com",
         "aud":"http://auth.example.com",
         "exp":"1361398824",
         "nbf":"1360189224",
         "cnf":{
            "jwk" : {
              "kty" : "EC",
              "kid" : h'11',
              "crv" : "P-256",
              "x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
              "y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
            }
          }
        }

      Figure 8: Example: Access Token Structure (Asymmetric Variant)

   Note: In this example there is no need for the authorization server
   to convey further keying material to the client since the client is
   already in possession of the private key (as well as the public key).

5.  Security Considerations

   [21] describes the architecture for the OAuth 2.0 proof-of-possession
   security architecture, including use cases, threats, and
   requirements.  This requirements describes one solution component of
   that architecture, namely the mechanism for the client to interact
   with the authorization server to either obtain a symmetric key from
   the authorization server, to obtain an asymmetric key pair, or to
   offer a public key to the authorization.  In any case, these keys are
   then bound to the access token by the authorization server.

   To summarize the main security recommendations: 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 (see Section 2.2 of [10] for
   a description about how symmetric keys can be securely conveyed
   within the access token) this symmetric key MUST be encrypted by the
   authorization server with a long-term key shared with the resource
   server.

   To deal with token redirect, 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



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   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 OAuth 2.0 proof-of-possession
   security model completely insecure.  OAuth 2.0 [2] relies on TLS to
   offer confidentiality protection and additional protection can be
   applied using the JWK [5] offered security mechanism, which would add
   an additional layer of protection on top of TLS for cases where the
   keying material is conveyed, for example, to a hardware security
   module.  Which version(s) of TLS ought to be implemented will vary
   over time, and depend on the widespread deployment and known security
   vulnerabilities at the time of implementation.  At the time of this
   writing, TLS version 1.2 [4] is the most recent version.  The client
   MUST validate the TLS certificate chain when making requests to
   protected resources, including checking the validity of the
   certificate.

   Similarly to the security recommendations for the bearer token
   specification [16] 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 smart phone app
   and Web development environments.

   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.  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).





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   When authorization servers bind symmetric keys to access tokens then
   they SHOULD scope these access tokens to a specific permissions.

6.  IANA Considerations

6.1.  OAuth Access Token Types

   This specification registers the following error in the IANA "OAuth
   Access Token Types" [24] established by [16].

   o  Name: pop
   o  Change controller: IESG
   o  Specification document(s): [[ this specification ]]

6.2.  OAuth Parameters Registration

   This specification registers the following value in the IANA "OAuth
   Parameters" registry [24] established by [2].

   o  Parameter name: cnf_req
   o  Parameter usage location: authorization request, token request
   o  Change controller: IESG
   o  Specification document(s): [[ this specification ]]

   o  Parameter name: cnf
   o  Parameter usage location: authorization response, token response
   o  Change controller: IESG
   o  Specification document(s): [[ this specification ]]

   o  Parameter name: rs_cnf
   o  Parameter usage location: token response
   o  Change controller: IESG
   o  Specification document(s): [[ this specification ]]

6.3.  OAuth Extensions Error Registration

   This specification registers the following error in the IANA "OAuth
   Extensions Error Registry" [24] established by [2].

   o  Error name: invalid_token_type
   o  Error usage location: implicit grant error response, token error
      response
   o  Related protocol extension: token_type parameter
   o  Change controller: IESG
   o  Specification document(s): [[ this specification ]]






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7.  Acknowledgements

   We would like to thank Chuck Mortimore for his review comments.

8.  References

8.1.  Normative References

   [1]        Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [2]        Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/info/rfc6749>.

   [3]        Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [4]        Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [5]        Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <https://www.rfc-editor.org/info/rfc7517>.

   [6]        Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [7]        Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [8]        Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <https://www.rfc-editor.org/info/rfc7516>.

   [9]        Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.





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   [10]       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,
              <https://www.rfc-editor.org/info/rfc7800>.

   [11]       Jones, M. and N. Sakimura, "JSON Web Key (JWK)
              Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
              2015, <https://www.rfc-editor.org/info/rfc7638>.

   [12]       Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
              Tschofenig, "Proof-of-Possession Key Semantics for CBOR
              Web Tokens (CWTs)", draft-ietf-ace-cwt-proof-of-
              possession-03 (work in progress), June 2018.

   [13]       Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
              "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
              May 2018, <https://www.rfc-editor.org/info/rfc8392>.

   [14]       Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

   [15]       Campbell, B., Bradley, J., and H. Tschofenig, "Resource
              Indicators for OAuth 2.0", draft-ietf-oauth-resource-
              indicators-01 (work in progress), October 2018.

8.2.  Informative References

   [16]       Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750,
              DOI 10.17487/RFC6750, October 2012,
              <https://www.rfc-editor.org/info/rfc6750>.

   [17]       Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [18]       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, <https://www.rfc-editor.org/info/rfc7521>.

   [19]       Sakimura, N., Ed., Bradley, J., and N. Agarwal, "Proof Key
              for Code Exchange by OAuth Public Clients", RFC 7636,
              DOI 10.17487/RFC7636, September 2015,
              <https://www.rfc-editor.org/info/rfc7636>.




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   [20]       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,
              <https://www.rfc-editor.org/info/rfc7591>.

   [21]       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-08 (work
              in progress), July 2016.

   [22]       Richer, J., Ed., "OAuth 2.0 Token Introspection",
              RFC 7662, DOI 10.17487/RFC7662, October 2015,
              <https://www.rfc-editor.org/info/rfc7662>.

   [23]       Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
              H. Tschofenig, "Authentication and Authorization for
              Constrained Environments (ACE) using the OAuth 2.0
              Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-16
              (work in progress), October 2018.

   [24]       IANA, "OAuth Parameters", October 2018.

   [25]       IANA, "JSON Web Token Claims", June 2018.

Authors' Addresses

   John Bradley
   Ping Identity

   Email: ve7jtb@ve7jtb.com
   URI:   http://www.thread-safe.com/


   Phil Hunt
   Oracle Corporation

   Email: phil.hunt@yahoo.com
   URI:   http://www.indepdentid.com


   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/






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   Hannes Tschofenig
   Arm Ltd.
   Absam  6067
   Austria

   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at


   Meszaros Mihaly
   NIIF Institute
   Hungary

   Email: misi@niif.hu





































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