OAuth Working Group                                             D. Hardt
Internet-Draft                                                    Amazon                                             July 03, 2019
Intended status: Standards Track                        October 19, 2018
Expires: April 22, 2019 January 4, 2020

                            Reciprocal OAuth


   There are times when a user has a pair of protected resources that
   would like to request access to each other.  While OAuth flows
   typically enable the user to grant a client access to a protected
   resource, granting the inverse access requires an additional flow.
   Reciprocal OAuth enables a more seamless experience for the user to
   grant access to a pair of protected resources.

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1.  Introduction

   In the usual three legged, authorization code grant, the OAuth flow
   enables a resource owner (user) to enable a client (party A) to be
   granted authorization to access a protected resource (party B).  If
   party A also has a protected resource that the user would like to let
   party B access, then a second complete OAuth flow, but in the reverse
   direction, must be performed.  In practice, this is a complicated
   user experience as the user is at Party A, but the OAuth flow needs
   to start from Party B.  This requires the second flow to send the
   user back to party B, which then sends the user to Party A as the
   first step in the flow.  At the end, the user is at Party B, even
   though the original flow started at Party A.

   Reciprocal OAuth simplifies the user experience by eliminating the
   redirections in the second OAuth flow.  After the intial OAuth flow,
   party A obtains consent from the user to grant party B access to a
   protected resource at party A, and then passes an authorization code
   to party B using the access token party A obtained from party B to
   provide party B the context of the user.  Party B then exchanges the
   authorization code for an access token per the usual OAuth flow.

1.1.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119

2.  Reciprocol Protocol Flow
    Party A                                         Party B
    +---------------+                               +---------------+
    |               |--(A)- Authorization Request ->|   Resource    |
    |               |                               |   Owner B     |
    |               |<-(B)-- Authorization Grant ---|               |
    |               |                               +---------------+
    |   Client A    |
    |               |                               +---------------+
    |               |--(C)-- Authorization Grant -->|               |
    |               |                               | Authorization |
    |               |<-(D)---- Access Token B ------|   Server B    |
    |               |       Reciprocol Request      |               |
    +---------------+                               +---------------+
   Reciprocol Request
    +---------------+                               +---------------+
    |   Resource    |                               | Authorization |
    |   Owner A     |--(E)--- Reciprocol Grant ---->|   Server B    |
    |               |          Access Token B       |               |
    +---------------+                               +---------------+
                                                    Reciprocol Grant
    +---------------+                               +---------------+
    |               |<-(F)--- Reciprocol Grant -----|               |
    | Authorization |                               |   Client B    |
    |  Server A     |--(G)---- Access Token A ----->|               |
    +---------------+                               +---------------+

    Figure 1: Abstract Reciprocol Protocol Flow

   The reciprocol authorization between party A and party B are
   abstractly represented in Figure 1 and includes the following steps:

   o  (A - C) are the same as in [RFC6749] 1.2

   o  (D) Party B optionally includes the reciprocol scope in the
      See Section 2.1 for details.

   o  (E) Party A sends the reciprocol authorization grant to party B.
      See Section 2.2.2 for details.

   o  (F) Party B requests an access token, mirroring step (B)

   o  (G) Party A issues an access token, mirroring step (C)

2.1.  Reciprocal Scope Request

   When party B is providing an access token response per [RFC6749]
   4.1.4, 4.2.1, 4.3.3 or 4.4.3, party B MAY include an additional query
   component in the redirection URI to indicate the scope requested in
   the reciprocal grant. grant:

     The scope of party B's reciprocal access request per [RFC6749] 3.3.

   If party B does not provide a reciprocal parameter in the access
   token response, the reciprocal scope will be a value previously
   preconfigured by party A and party B.

   If an authorization code grant access token response per [RFC6749]
   4.1.4, an example successful response: response (with extra line breaks for
   display purposes only):

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


   If an authorization code grant access token response per [RFC6749]
   4.2.2, an example successful response (with extra line breaks for
   display purposes only):

   HTTP/1.1 302 Found
   Location: http://example.com/cb#


   When party B is providing an authorization response per [RFC6749]
   4.1.2, party B MAY include an additional query component in the
   redirection URI to indicate the scope requested in the reciprocal

   reciprocal OPTIONAL.  The scope of party B's reciprocal access
   request per [RFC6749] 3.3.

   If party B does not provide a reciprocal parameter in the
   authorization response, the reciprocal scope will be a value
   previously preconfigured by party A and party B.

2.2.  Reciprocal Authorization Flow

   The reciprocal authorization flow starts after the client (party A)
   has obtained an access token from the authorization server (party B)
   per [RFC6749] 4.1 Authorization Code Grant.


2.2.1.  User Consent

   Party A obtains consent from the user to grant Party B access to
   protected resources at party A.  The consent represents the scopes
   requested by party B had preconfigured at from party A.

3.2. A per Section 2.1.

2.2.2.  Reciprocal Authorization Code

   Party A generates an authorization code representing the access
   granted to party B by the user.  Party A then makes a request to
   party B's token endpoint authenticating per [RFC6749] 2.3 and sending
   the following parameters using the "application/x-www-form-
   urlencoded" format per [RFC6749] Appendix B with a character encoding
   of UTF-8 in the HTTP request entity-body:

     Value MUST be set to "urn:ietf:params:oauth:grant-type:reciprocal".

     the authorization code generated by party A.

     party A'a client ID.

   access_token REQUIRED, REQUIRED the access token obtained from Party B.  Used
   by Party B to provide identify which user context. authorization is being requested.

   For example, the client makes the following HTTP request using TLS
   (with extra line breaks for display purposes only):

    POST /token HTTP/1.1
    Host: server.example.com
    Authorization: Basic ej4hsyfishwssjdusisdhkjsdksusdhjkjsdjk
    Content-Type: application/x-www-form-urlencoded



   Party B MUST verify the authentication provided by Party A per
   [RFC6749] 2.3

   Party B MUST then verify the access token was granted to the client
   identified by the client_id.

   Party B MUST respond with either an HTTP 200 (OK) response if the
   request is valid, or an HTTP 400 "Bad Request" if it is not.

   Party B then plays the role of the client to make an access token
   request per [RFC6749] 4.1.3.


3.  Authorization Update Flow

   After the initial authorization, the user may add or remove scopes
   available to the client at the authorization server.  For example,
   the user may grant additional scopes to the client using a voice
   interface, or revoke some scopes.  The authorization server can
   update the client with the new authorization by sending a new
   authorization code per 3.2.

5. Section 2.2.2.

4.  IANA Considerations



5.  Acknowledgements



6.  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,

   [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,

Appendix A.  Document History

A.1.  draft-ietf-oauth-reciprical-00

   o  Initial version.

A.2.  draft-ietf-oauth-reciprical-01

   o  changed  Changed reciprocal scope request to be in access token response
      rather than authorization request

A.3.  draft-ietf-oauth-reciprical-02

   o  Added in diagram to clarify protocol flow

Author's Address

   Dick Hardt

   Email: dick.hardt@gmail.com