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Versions: 00                                                            
OAUTH                                                     J. Richer, Ed.
Internet-Draft                                       Bespoke Engineering
Intended status: Standards Track                            21 June 2021
Expires: 23 December 2021

     OAuth Proof of Possession Tokens with HTTP Message Signatures


   This extension to the OAuth 2.0 authorization framework defines a
   method for using HTTP Message Signatures to bind access tokens to
   keys held by OAuth 2.0 clients.

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 23 December 2021.

Copyright Notice

   Copyright (c) 2021 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
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   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Token Response  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Presenting an HTTP Message Signature Bound Access Token . . .   3
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The OAuth 2.0 framework provides methods for clients to get delegated
   access tokens from an authorization server for accessing protected
   resources.  The access tokens at the center of OAuth 2.0 can be bound
   to a variety of different mechanisms, including bearer tokens, mutual
   TLS, or other presentation mechanisms.

   Bearer tokens are simple to implement but also have the significant
   security downside of allowing anyone who sees the access token to use
   that token.  This extension defines a token type that binds the token
   to a presentation key known to the client.  The client uses HTTP
   Message Signatures (I-D.ietf-httpbis-message-signatures) to sign
   requests using its key, thereby proving its right to present the
   associated access token.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document contains non-normative examples of partial and complete
   HTTP messages, JSON structures, URLs, query components, keys, and
   other elements.  Some examples use a single trailing backslash '' to
   indicate line wrapping for long values, as per [RFC8792].  The "\"
   character and leading spaces on wrapped lines are not part of the

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2.  Token Response

   When the client makes an access token request, the AS associates the
   generated access token with the client's registered key from the
   client's "jwks" or "jwks_uri" field.  All presentations of this token
   at any RS MUST contain an HTTP message signature as described in
   Section 3.

   A bound access token MUST have a "token_type" value of "httpsig".
   The response MUST contain a "keyid" value which indicates the key the
   client MUST use when presenting the access token Section 3.  The
   value of this "keyid" field MUST uniquely identify a key from the
   client's registered key set by its "kid" value.

       "access_token": "2340897.34j123-134uh2345n",
       "token_type": "httpsig",
       "keyid": "test-key-rsa-pss"

   [[ Editor's note: while this document deals only with using a pre-
   registered key, it would be possible to have different key binding
   mechanisms, such as the client presenting an ephemeral key during the
   token request or the AS generating and assigning a key alongside the
   token.  The WG needs to decide if this is in scope of this document
   or not.  The presentation mechanisms would be the same. ]]

3.  Presenting an HTTP Message Signature Bound Access Token

   The algorithm and key used for the HTTP Message Signature are derived
   from the client's registered information.  The key is taken from the
   client's registered "jwks" or "jwks_uri" field, identified by the
   "keyid" field of the token response Section 2.  The signature
   algorithm is determined by the "alg" field of the identified key,
   following the method for JSON Web Algorithm selection described in

   The client MUST include the access token value in an "Authorization"
   header using scheme "HTTPSig".  Note that the scheme value "HTTPSig"
   is not case sensitive.

   Authorization: HTTPSig 2340897.34j123-134uh2345n

   The client MUST include an HTTP Message Signature that covers, at

   *  The request target of the RS being called

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   *  The "Host" header of the RS being called

   *  The "Authorization" header containing the access token value.

   The signature parameters MUST include a "created" signature
   parameter.  The RS SHOULD use this field to ensure freshness of the
   signed request, appropriate to the API being protected.

   The client MUST NOT include an "alg" signature parameter, since the
   algorithm is determined by the client's registered key.  The client
   MUST include the "keyid" signature parameter set to the value
   returned in the token response Section 2.

   In this example, the client has a key with the "kid" value of "test-
   key-rsa-pss" which uses the JWA "alg" value of "PS512".  The
   signature input string is:

   "@request-target": get /foo
   "host": example.org
   "authorization": HTTPSig 2340897.34j123-134uh2345n
   "@signature-params": ("@request-target" "host" "authorization")\

   This results in the following signed HTTP message, including the
   access token.

   GET /foo HTTP/1.1
   Host: example.com
   Date: Tue, 20 Apr 2021 02:07:55 GMT
   Authorization: HTTPSig 2340897.34j123-134uh2345n
   Signature-Input: sig1=("@request-target" "host" "authorization")\
   Signature: sig1=:o+Fy/a6IIWhHwnMFhsHqfXEpheWGBMOU3pheT50zA8rL5F8Nur\

   An RS receiving such a signed message and a bound access token MUST
   verify the HTTP Message Signature as described in
   [I-D.ietf-httpbis-message-signatures].  The RS MUST verify that all
   required portions of the HTTP request are covered by the signature by
   examining the contents of the signature parameters.

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   [[ Editor's note: we should define confirmation methods for access
   tokens here, including JWT values and introspection response values
   to allow the RS to verify the signature w/o the client's registration
   information. ]]

4.  Acknowledgements

5.  IANA Considerations

   [[ TBD: register the token type and new parameters into their
   appropriate registries, as well as the JWT and introspection
   parameters. ]]

6.  Security Considerations

   [[ TBD: There are a lot of security considerations to add. ]]

   All requests have to be over TLS or equivalent as per [BCP195].

7.  Privacy Considerations

   [[ TBD: There are a lot of privacy considerations to add. ]]

8.  Normative References

   [BCP195]   Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", May 2015,

              Backman, A., Richer, J., and M. Sporny, "Signing HTTP
              Messages", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-message-signatures-05, 8 June 2021,

              Fett, D., Campbell, B., Bradley, J., Lodderstedt, T.,
              Jones, M., and D. Waite, "OAuth 2.0 Demonstrating Proof-
              of-Possession at the Application Layer (DPoP)", Work in
              Progress, Internet-Draft, draft-ietf-oauth-dpop-03, 7
              April 2021, <https://www.ietf.org/archive/id/draft-ietf-

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              Lodderstedt, T., Richer, J., and B. Campbell, "OAuth 2.0
              Rich Authorization Requests", Work in Progress, Internet-
              Draft, draft-ietf-oauth-rar-05, 15 May 2021,

              Richer, J., Bradley, J., and H. Tschofenig, "A Method for
              Signing HTTP Requests for OAuth", Work in Progress,
              Internet-Draft, draft-ietf-oauth-signed-http-request-03, 8
              August 2016, <https://www.ietf.org/archive/id/draft-ietf-

              Backman, A. and M. Scurtescu, "Subject Identifiers for
              Security Event Tokens", Work in Progress, Internet-Draft,
              draft-ietf-secevent-subject-identifiers-08, 24 May 2021,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3230]  Mogul, J. and A. Van Hoff, "Instance Digests in HTTP",
              RFC 3230, DOI 10.17487/RFC3230, January 2002,

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,

   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <https://www.rfc-editor.org/info/rfc5646>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750,
              DOI 10.17487/RFC6750, October 2012,

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   [RFC7234]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
              RFC 7234, DOI 10.17487/RFC7234, June 2014,

   [RFC7468]  Josefsson, S. and S. Leonard, "Textual Encodings of PKIX,
              PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468,
              April 2015, <https://www.rfc-editor.org/info/rfc7468>.

   [RFC7515]  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>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,

   [RFC8705]  Campbell, B., Bradley, J., Sakimura, N., and T.
              Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
              and Certificate-Bound Access Tokens", RFC 8705,
              DOI 10.17487/RFC8705, February 2020,

   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
              "Handling Long Lines in Content of Internet-Drafts and
              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,

Appendix A.  Document History

   *  -00

      -  Initial individual draft.

Author's Address

   Justin Richer (editor)
   Bespoke Engineering

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   Email: ietf@justin.richer.org
   URI:   https://bspk.io/

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