Add response codes for error scenarios

[garciasolero]

What type of PR is this?

• documentation

What this PR does / why we need it:

We know that many scenarios are already conveniently explained in the documentation of various standards, but a new section compiling errors and their scenarios from several specifications would reduce misunderstandings and potential interoperability issues between operators.

Which issue(s) this PR fixes:

Fixes #211

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: garciasolero / name: Juan Fabio García Solero (2b429dc, 8896ce8, 56f35f0)

[jpengar]

LGTM

[eric-murray]

Following discussion at the TSC meeting last week, we need to be clear which parts of our documents are normative and which are informative.

So is this new section intended to be normative? - i.e. it will apply, even if it turns out that OIDC says something different compared to this section.

Or is it informative? So a summary of how we think OIDC errors apply to the CAMARA scenario, but OIDC remains normative?

The use of "MUST" in the first sentence implies normative, in which case, that status should be added in brackets to the section header e.g. "Appendix A (Normative) : Error Responses"

[jpengar]

As discussed in the last WG call, this proposal is to make the definitions of error scenarios normative.

[eric-murray]

Suggested change

	## Appendix A: Error Responses
	## Appendix A (Normative): Error Responses

[AxelNennker]

Can we be more specific on how the authorization server informs the resource owner? This section repeats what is already defined in OIDC, OAuth2 and CIBA. Why does it not mention invalid_request_uri?

[garciasolero]

As far as I know, the only suggestion ever made was to send the request object by value, not by reference. So this error would not occur as it would return request_uri_not_supported.

Added clarification about how to inform resource owner when no redirection.

[trehman-gsma]

I think this new section is valuable, particularly for implementor technical teams we've spoken to that are not so close to OpenID specification, and for integrators who can use it as a concise requirements guide. I think it would be helpful if the sub-sections linked out to the relevant OIDC Error specification for readers to review the full context of the expected error response (e.g. Authentication Error Response). For example, in Auth Code flow, there are other parameters that can be returned (e.g. a state parameter may be required depending on the input).

[garciasolero]

I added new links to relevant error specifications.