Define error when fetch can't service requested issuer

[Michael Jones]

While working on proposed Certification tests, I discovered that we don’t say what error a fetch endpoint should return if it cannot issue Entity Statements for the requested “iss” value. I propose that we add an “invalid_issuer” value to the set of error codes at https://openid.net/specs/openid-federation-1_0-34.html#error_response.

[Giuseppe De Marco]

it makes sense

[Michael Jones]

To be fixed by https://bitbucket.org/openid/connect/pull-requests/735

[Michael Jones]

Fixed by https://bitbucket.org/openid/connect/pull-requests/735