[Openid-specs-ab] inconsistent treatment of id_token_hint?

[John Bradley]

Well it MUST be consistent.

I think it was MUST in both places then there was a discussion that it is the responsibility of the client to check the sub in the returned id_token, so it may be better in some cases to have the IdP respond with a positive response for a diffrent sub rather than an error.   

Saying both would be the worst of both worlds.

If we are certain that RP really validate the sub in prompt=none cases then SHOULD is fine.   If clients are sloppy with that then having it a MUST is better as it will stop clients from mistakenly thinking that a positive response is fro the same user.

I think I was the one arguing for MUST at the time, but I tend to be conservative.

We must have missed the other reference when it was changed to SHOULD.

John B.
> On Apr 7, 2015, at 8:10 AM, Brian Campbell <bcampbell at pingidentity.com> wrote:
> 
> Core has two mentions of id_token_hint (not counting self issued and IANA registration), which are quoted 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.
> Is this an oversight that should maybe be fixed in errata v.next? 
> 
> Or is there something more subtle or intentional here?
> 
> 
> http://openid.net/specs/openid-connect-core-1_0.html#AuthRequest <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 <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 <http://openid.net/specs/openid-connect-core-1_0.html#IndividualClaimsRequests>, if the claims parameter is supported by the implementation.
> 
> 
> 
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