[Federation] Support explicit client registration request with Trust Chain

[Vladimir Dzhuvinov]

Proposal by @Torsten Lodderstedt to support explicit client registration by passing a complete Trust Chain instead of an Entity Configuration only:

https://bitbucket.org/openid/connect/pull-requests/286#comment-325466353

The processing is identical to the optional trust_chain parameter in automatic registration.

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[Vladimir Dzhuvinov]

HTTP requests with a trust chain will need to have a new Content-Type defined.

For HTTP requests with an Entity Configuration the Content-Type is application/entity-statement+jwt

[Takahiko Kawasaki]

application/x-www-form-urlencoded with a form parameter trust_chain with a value in the format of JSON array (like authorization_details defined in RAR), for example?

[Michael Jones]

On the 25-Aug-22 Federation Editors' Call, @Giuseppe De Marco agreed to create a new PR to do this. We agreed to not repeat the Entity Statement if it is already included in the trust chain. So one could register either with an Entity Configuration or a trust chain.

[Giuseppe De Marco]

I’d wait for the merge of https://bitbucket.org/openid/connect/pull-requests/286 before add trust_chain also in the explicit client registration.

The registration request can be submitted with two different Content-Type: application/entity-statement+jwt and application/json
The first contains the Entity Configuration of the requesting RP, the second is an json array containing the sequence of statements that forms the trust_chain.

the ordering of the trust chains statements is described in the Trust Chain Section.

[Michael Jones]

Time for a PR for this now that PR #286 and PR #289 have been merged!

[Giuseppe De Marco]

This issue will be closed by this PR
https://bitbucket.org/openid/connect/pull-requests/297/feat-federation-trust-chain-in-explicit

[Michael Jones]

This was fixed by https://bitbucket.org/openid/connect/pull-requests/297/feat-federation-trust-chain-in-explici