[OpenID-Specs-eKYC-IDA] Issue #1301: convey error response in userinfo (openid/ekyc-ida)

[Kosuke Koiwai]

New issue 1301: convey error response in userinfo
https://bitbucket.org/openid/ekyc-ida/issues/1301/convey-error-response-in-userinfo

Kosuke Koiwai:

There were discussions in OIDF-Japan that there is a need to return an error response in the userinfo endpoint.

An IDP provides social-login service and ID verification service. When an RP wants to authenticate user \(with `sub`\) AND get  `verified_claims` when possible, the RP wants to know the reason why it didn't receive `verified_claims` from userinfo response. Here the RP still wants to get `sub` to authenticate user, so returning an error in authorization response is not sufficient.

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