Simplify dynamic client registration with custom metadata

[dsukhoroslov]

Expected Behavior

• RegisteredClient/OidcClientRegistration classes should provide access any Client Metadata parameters as per OIDC DCR spec
• RegisteredClientRepository should be able to store and retrieve any custom Client Metadata parameters.

Current Behavior

• Current DCR implementation supports only limited set of Client Metadata parameters

Context
in our project we need to register clients with some additional parameters which used in communication with downstream systems. It should be possible as per OIDC DCR spec, but the current implementation supports only limited set of Client Metadata parameters (even not custom, but specified in the spec). Could you consider to extend the current DCR implementation a bit? The most flexible way would be to store initial Client Registration request body as raw JSON string in DB and also provide access to it in RegistreredClient/OidcClientRegistration classes with generic Map<String, Object> interface, probably. Some CustomClientMetadataValidator component could be also useful to be able to customise Client Metadata validation.

[jgrandja]

@dsukhoroslov It's already possible to store custom client metadata during dynamic client registration and access it from RegisteredClient. I've added the following test to demonstrate usage:

spring-authorization-server/oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/config/annotation/web/configurers/OidcClientRegistrationTests.java

Line 412 in b6ff06d

public void requestWhenClientRegistersWithCustomMetadataThenSavedToRegisteredClient() throws Exception {

You will notice some code duplication in the test so we'll look at improving it. If there is anything else you would like to suggest for improvement please let us know.

[dsukhoroslov]

@jgrandja thank you so much for the hint, using it I was able to store custom client metadata in RegisteredClient. if Converter would be public and not final then it should be possible just to extend it and not duplicate its code, probably..

[jgrandja]

@dsukhoroslov I'm glad it worked out 👍

I'm going to re-open this issue as we will likely make the Converter public to allow for better reuse.

[dsukhoroslov]

ah, ok 👍

[ddubson]

@jgrandja - may I request assignment on this issue?

[ddubson]

@jgrandja - as part of my research on this enhancement, I realized I can easily address #647 as well as it is directly related. Thoughts on that?

[jgrandja]

@ddubson That would be great. But let's keep them separate and submit as separate PR's. Thanks.