OAuth updates vol 5

[elarlang]

This Pull Request relates to issues:

• V51, Verify usage of the "iss" parameter in by the authorization server #2095
• V51 OAuth: Add verifications for Authorization Server client configuration  #2043
• Add requirement about usage of claims other than subject and issuer as an identifier for OpenID Connect #1826

[tghosth]

Approved with my language tweaks @elarlang so merge if you are ready

[elarlang]

Approved with my language tweaks @elarlang so merge if you are ready

51.2.8 seems not finished.

also I think 51.3.6 requires the "in requests to the authorization server", just "from authorization server" is too wide.

[tghosth]

Yeah what I didn't love about "in requests to the authorization server" is that it uses the word requests again in a different context but I can live with it if you want to merge like this.

[elarlang]

All those V51 requirements need some ironing and style/wording/terminology alignment fixes, at the moment the main goal is to get the clear requirement ideas/points in.