OAuth Working Group D. Hardt
Internet-Draft July 23, 2019
Intended status: Standards Track
Expires: January 24, 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.

For example, a user would like their voice assistant (party A) and music service (party B) to work together. The voice assistant wants to call the music service to play music, and the music service wants to call the voice assistant with music information to present to the user. The user starts the OAuth flow at the voice assistant, and is redirected to the music service. The music services obtains consent from the user and the redirects back to the voice assistant. At this point the voice assistant is able to obtain an access token for the music service. The voice assistant can the get consent from the user to authorize the music service to access the voice assistant, and then the voice assistant can create an authorization code and send it to the music service, which then exchanges the authorization code for an access token, all without further user interaction. Note that either the voice assistant or the music service can initiate the flow, so that either can prompt the user for the two parties to work together.

1.1. Terminology

In this document, the key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” are to be interpreted as described in BCP 14, RFC 2119 [RFC2119].

2. reciprocal 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    |
 |               |       reciprocal Request      |               |
 +---------------+                               +---------------+
reciprocal Request
 +---------------+                               +---------------+
 |   Resource    |                               | Authorization |
 |   Owner A     |--(E)--- reciprocal Grant ---->|   Server B    |
 |               |          Access Token B       |               |
 +---------------+                               +---------------+
                                                 reciprocal Grant
 +---------------+                               +---------------+
 |               |<-(F)--- reciprocal Grant -----|               |
 | Authorization |                               |   Client B    |
 |  Server A     |--(G)---- Access Token A ----->|               |
 +---------------+                               +---------------+

 Figure 1: Abstract reciprocal Protocol Flow

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

Note that Resource Owner A and Resource Owner B are the respective resource owner interaction systems controlled by the same owner.

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:

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 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 (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 grant.

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 from party 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:

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

    the authorization code generated by party A.

client_id REQUIRED
    party A'a client ID.

access_token REQUIRED the access token obtained from Party B. Used by Party B to identify which user 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 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., "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-reciprocal-00

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

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

A.4. draft-ietf-oauth-reciprocal-03

Author's Address

Dick Hardt EMail: dick.hardt@gmail.com

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