[Openid-specs-ab] Issue #968: inconsistent treatment of id_token_hint (openid/connect)

[Brian Campbell]

New issue 968: inconsistent treatment of id_token_hint
https://bitbucket.org/openid/connect/issue/968/inconsistent-treatment-of-id_token_hint

Brian Campbell:

Core has two mentions of id_token_hint (not counting self issued and IANA registration), which are pasted below. It seems that one says that an error SHOULD be returned if the end-user identified by the id_token_hint isn't the current user while the other says an error MUST be returned.

The spec **should** be consistent with itself. 

The thread starting [here](http://lists.openid.net/pipermail/openid-specs-ab/Week-of-Mon-20150406/005492.html ) is about the issue and has some opinions on SHOULD vs. MUST. I'd think the latter is preferable. 

http://openid.net/specs/openid-connect-core-1_0.html#AuthRequest

id_token_hint
    OPTIONAL. ID Token previously issued by the Authorization Server being passed as a hint about the End-User's current or past authenticated session with the Client. If the End-User identified by the ID Token is logged in or is logged in by the request, then the Authorization Server returns a positive response; otherwise, it SHOULD return an error, such as login_required. When possible, an id_token_hint SHOULD be present when prompt=none is used and an invalid_request error MAY be returned if it is not; however, the server SHOULD respond successfully when possible, even if it is not present. The Authorization Server need not be listed as an audience of the ID Token when it is used as an id_token_hint value. 


http://openid.net/specs/openid-connect-core-1_0.html#AuthRequestValidation

If the sub (subject) Claim is requested with a specific value for the ID Token, the Authorization Server MUST only send a positive response if the End-User identified by that sub value has an active session with the Authorization Server or has been Authenticated as a result of the request. The Authorization Server MUST NOT reply with an ID Token or Access Token for a different user, even if they have an active session with the Authorization Server. Such a request can be made either using an id_token_hint parameter or by requesting a specific Claim Value as described in Section 5.5.1, if the claims parameter is supported by the implementation.