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OAuth Working Group                                          N. Sakimura
Internet-Draft                                 Nomura Research Institute
Intended status: Standards Track                               N. Matake
Expires: May 19, 2018                                         GREE, Inc.
                                                            S. Preibisch
                                                         CA Technologies
                                                       November 15, 2017


                        OAuth Response Metadata
                      draft-sakimura-oauth-meta-08

Abstract

   This specification defines an extensible metadata framework that may
   be inserted into the OAuth 2.0 responses to assist the clients to
   process those responses.  It is expressed either as a link header, or
   query parameters.  It will allow the client to learn the metadata
   about the particular response.  For example, the client can learn
   where the members in the response could be used, what is the
   characteristics of the payload is, how it should be processed, and so
   on.  Since they are just additional response header/query parameters,
   any client that does not understand this extension should not break
   and work normally while supporting clients can utilize the metadata
   to take the advantage of the extension.

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 May 19, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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
     1.1.  Requirements Notation and Conventions . . . . . . . . . .   3
     1.2.  terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Resource Endpoint Resonse . . . . . . . . . . . . . . . . . .   3
   3.  Token Endpoint Response . . . . . . . . . . . . . . . . . . .   4
   4.  Authorization Endpoint HEAD response  . . . . . . . . . . . .   5
   5.  Authorization Response  . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Link Type Registration  . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
     7.1.  Authorization Response Query Parameter Tampering by a Bad
           User  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   9.  Document History  . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informational References . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Although OAuth 2.0 [RFC6749] has been known for its REST
   friendliness, OAuth itself is not RESTful, as it heavily relies on
   out-of-band information to drive the interactions.  This situation
   can be eased by hypertext-enabling the endpoint responses through the
   introduction of data structure that represents such hypertext and
   other metadata.

   Hyper-text enabling the OAuth responses has many advantages.  For
   example,

   o  The protected resource can tell which authorization servers it
      supports.

   o  Permissioned resource discovery: It is possible to tell the client
      which resource endpoint it should use.  This has a privacy



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      advantage.  The location of the resource by itself may be a
      sensitive information as its location may reveal information about
      the resource owner.  Therefore, it may be sensible to tell the
      location only after the user consent.

   o  It is possible to give a hint on the processing of the payload.

   o  It will be resitant to IdP Mix-up attack.

   o  It will be resitant to Code Phishing Attack.

   This specification defines methods to represent such metadata in the
   authorization and token responses.

1.1.  Requirements Notation and Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

1.2.  terminology

   This specification uses the terms "Access Token", "Authorization
   Code", "Authorization Endpoint", "Authorization Grant",
   "Authorization Server", "Client", "Client Authentication", "Protected
   Resource", "Refresh Token", and "Token Endpoint" defined by OAuth 2.0
   [RFC6749].

2.  Resource Endpoint Resonse

   Resource Endpoints that implement this specification returns the
   following link relation (rel) and the corresonding URI value as
   defined in [RFC5988] in the response header.  The response header can
   be returned in response to HEAD, GET, or POST request to the
   endpoint.

   duri  The URI of the corresponding authorization server's discovery
      document, from which the client can learn the server capabilities
      and endpoints.

   auri  The URI of the corresponding Authorization Endpoint URI.

   A typical example of the use of these header values are in the case
   of the Client accessing the protected resource without a propoer
   credential.  For example, in the case of an [RFC6750] protected
   resource, the unauthorized access may result in a response header
   that includes both WWW-Authenticate header as well as the Web Linking




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   header indicating either the Authorization Endpoint URI or the
   discovery document URI.

   There is no cardinality restriction on relations put in place by
   [RFC5988].  Therefore, the resource can respond with multiple
   Authorization Endpoint URI or Discovery Document URIs from which the
   Client may choose the appropriate one.

     HTTP/1.1 401 Unauthorized
     WWW-Authenticate: Bearer realm="example"
         Link: <https://example.com/.well-known/openid-configuration>; rel="duri",
         <https://example.net/.well-known/openid-configuration>; rel="duri",
         <https://example.com/authz/>; rel="auri",
         <https://example.net/az/>; rel="auri",
     <https://example.com/payment-upon-trial-expiry>; rel="payments"

3.  Token Endpoint Response

   Token Endpoints that implements this specification returns the
   following link relation (rel) and the corresponding URI value as
   defined in [RFC5988] in the Access Token Response defined in
   [RFC6749].

   ruri  Resource URI.  The value of this parameter is the URI of the
      Resource Endpoint that the Access Token is supposed to be used at.
      If this value is present, the client MUST NOT send the Access
      Token to any other URI.

   turi  Token Endpoint URI.  The value of this parameter is the URI of
      the Token Endpoint that the Refresh Token can be sent to obtain a
      new Access Token.  If this value is present, then the client MUST
      NOT send the refresh token to any other places.

   Any other rels that are registered in Link Relation Type Registry
   defined in [RFC5988] registry can be used.

   There is no cardinality restriction on relations put in place by
   [RFC5988].  Therefore, the Token Endpoing can respond with multiple
   Resource Endpoint URI or Discovery Document URIs from which the
   Client may choose the appropriate one.

   Following is an example of an HTTPS response.









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   HTTP/1.1 200 OK
   Link: <https://example.com/userinfo>; rel="ruri",
    <https://example.net/photostream/>; rel="ruri",
    <https://example.com/payment-upon-trial-expiry>; rel="payments"
   Content-Type: application/JSON; charset=utf-8

   {
           "access_token":"aCeSsToKen"
   }

4.  Authorization Endpoint HEAD response

   Authorization Endpoints that implements this specification returns
   the following link relation (rel) and the corresponding URI value as
   defined in [RFC5988] in the response to the HEAD request.

   auri  The canonical URI of the Authorization Endpoint URI.

   turi  Token Endpoint URI.  The value of this parameter is the URI of
      the Token Endpoint that the Authorization Code can be sent to
      obtain the Access Token.

   duri  The URI of discovery document, from which the client can learn
      the server capabilities and endpoints.

   ruri  Resource URI.  The value of this parameter is the URI of the
      Resource Endpoint that the Access Token can be used at.  If this
      parameter is specified, the client MUST NOT send the Access Token
      to any other URIs than the value of this parameter.

   There is no cardinality restriction on relations put in place by
   [RFC5988].  Therefore, the Authorization Endpoint can respond with
   multiple Endpoint URIs with a same relation type from which the
   Client may choose the appropriate one.

   Following is an example of an HTTPS response.

HTTP/1.1 200 OK
Link: <https://example.com/.well-known/openid-configuration>; rel="duri",
 <https://example.net/.well-known/openid-configuration>; rel="duri",
 <https://example.com/payment-upon-trial-expiry>; rel="payments"
Content-Type: application/JSON; charset=utf-8









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5.  Authorization Response

   While [RFC5988] defines a useful way of conveying link relations, it
   cannot be utilized for a redirect based communication such as the
   authorization response of OAuth 2.0.  This section defines a way to
   return a limited set of those link relations as query parameters so
   that it can be conveyed over the redirection.

   The authorization response of the implementation of this
   specification may return the following query parameter in the
   redirect URI.

   turi  Token Endpoint URI.  The value of this parameter is the URI of
      the Token Endpoint that the Authorization Code can be sent to
      obtain the Access Token.  If this parameter is specified, the
      client MUST check that the value of turi matches exactly with the
      pre-registered token endpoint URI of the Authorization Server that
      the session recoverd from the state variable points to.  The
      client MUST NOT send the code to any other URIs than the value of
      this parameter.

   ruri  Resource URI.  The value of this parameter is the URI of the
      Resource Endpoint that the Access Token can be used at.  If this
      parameter is specified, the client MUST NOT send the Access Token
      to any other URIs than the value of this parameter.

   As long as the link relation type string does not collide with the
   underlying protocol parameters, they can also be specified as a query
   parameter.  The value MUST be encoded in application/x-www-form-
   urlencoded.

   The following is an example of such response.  Line breaks are for
   display purposes only.

   HTTP/1.1 302 Found
   Location: https://client.example.com/cb?code=SplxlOBeZQQYbYS6WxSbIA
       &turi=https%3A%2F%2Fexample.com%2Ftoken
       &state=xyz

6.  IANA Considerations

6.1.  Link Type Registration

   Pursuant to [RFC5988], the following link type registrations [[will
   be]] registered by mail to link-relations@ietf.org.

   o  Relation Name: turi




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   o  Description: An OAuth 2.0 Token Endpoint specified in section 3.2
      of [RFC6749].

   o  Reference: This specification

   o  Relation Name: ruri

   o  Description: An OAuth 2.0 Resource Endpoint specified in section
      3.2 of [RFC6750].

   o  Reference: This specification

7.  Security Considerations

7.1.  Authorization Response Query Parameter Tampering by a Bad User

   The query response parameters may be tampered by the man-in-the-
   browser.  It can also be tampered by a malicious user.  In general,
   anything that comes via the browser/user-agent can be tainted and
   untrusted.

   This specification mandates the turi check so that tamparing of turi
   by the malicious user will be detected.  It does not mandate ruri
   check as the user can get the Access Token and send it to anywhere he
   wants anyways when it is returned to the browser.

   However, other parameters are not protected.  The Client MUST treat
   them tainted and implement its own check rules for each parameters.

   To solve this "Tampering by bad user", either HMAC(concat(params))
   need to be sent with them or have all of them inside the JWS.

8.  Acknowledgements

   Members of OAuth WG helped to form this specification.  Notabely:
   Hannes tschofenig, John Bradley, Justin Richer, Kaoru Maeda, Masashi
   Kurabayashi, Michael B.  Jones, Phil Hunt, William Dennis, James
   Manger, (add yourselves).

9.  Document History

   -07

   o  Added note that there is no cardinality requirements so that
      multiple endpoints can be returned by repeating a same rel.

   o  Added resource endpoint response.




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   -06

   o  Removed duri description from token response as it is not needed.

   o  Made the processing instruction more precise.

   o  Added RFC5988 defined link relation type in the example.

   o  Swaped the order of the authorization response and token response.
      Now, token response gets explained first so that the reader will
      grasp the basic concept according to RFC5988 and regards the
      authorization response extension as a mapping of RFC5988 into
      query parameter form.

   -05

   o  Factored out JSON Meta and now using query param and Web Linking.

   -04

   o  Date refresh.

   -03

   o  Date refresh.

   -02

   o  Added Mike Kelly as an author.

   o  xref fix.

   o  Introduced "operations" as in draft-ietf-scim-api-00#section-3.5.

   o  Updated the informative reference to HAL.

   o  Added description to OAuth Token Endpoint hrefs.

   o  Added content-type to the example.

   o  Added Area and Working Group.

   -01

   o  Some format changes, reference fix, and typo fixes.

   o  Changed 'items' to 'elements' to match the JSON terminology.




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   -00

   o  Initial Draft

10.  References

10.1.  Normative References

   [RFC2119]  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>.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616,
              DOI 10.17487/RFC2616, June 1999,
              <https://www.rfc-editor.org/info/rfc2616>.

   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988,
              DOI 10.17487/RFC5988, October 2010,
              <https://www.rfc-editor.org/info/rfc5988>.

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

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

10.2.  Informational References

   [HAL]      Kelly, M., "JSON Hypermedia API Language", February 2013.

   [oauth-lrdd]
              Mills, W., "Link Type Registrations for OAuth 2", October
              2012.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627,
              DOI 10.17487/RFC4627, July 2006,
              <https://www.rfc-editor.org/info/rfc4627>.







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   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570,
              DOI 10.17487/RFC6570, March 2012,
              <https://www.rfc-editor.org/info/rfc6570>.

Authors' Addresses

   Nat Sakimura
   Nomura Research Institute

   Email: sakimura@gmail.com


   Nov Matake
   GREE, Inc.

   Email: nov@matake.jp
   URI:   http://matake.jp


   Sascha Preibisch
   CA Technologies

   Email: Sascha.Preibisch@gmail.com



























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