Error code claims_not_supported should have been defined

[Michael Jones]

Discovery defines the feature tests claims_parameter_supported. request_parameter_supported, and request_uri_parameter_supported. Core defines the error values request_not_supported and request_uri_not_supported but it does not define claims_not_supported.

This omission came to light while considering what the corresponding certification tests should do. We should correct it at some point.

[Michael Jones]

We will say that it SHOULD be returned if not supported.

[Michael Jones]

Adding this error response would contradict this text in the spec:

"Should an OP not support this parameter and an RP uses it, the OP SHOULD return a set of Claims to the RP that it believes would be useful to the RP and the End-User using whatever heuristics it believes are appropriate."

Note that RPs can tell whether OPs supporting discovery support this request parameter with the "claims_parameter_supported" discovery value, so having this error code wouldn't add much functionality anyway.

We explicitly opted for functionality over adding this specific error. Therefore, I believe that we should resolve this issue as "invalid".