Support auto-configuration of JwkSet Uri

[jgrandja]

We should provide support for auto-configuration of the JwkSet Uri via the supplied issuer claim that can be used to discover Provider Metadata via OpenID Connect Discovery. The Provider Metadata contains the jwks_uri attribute which would be used to supply the JwtDecoder.

[jgrandja]

After this feature has been merged, we need to log a ticket with the Boot team to support the issuer configuration property.

[jgrandja]

@jzheaux As far as approach on implementing this feature, @rwinch and I spoke and agree that it should be implemented similar to how OidcConfigurationProvider.issuer() is implemented for ClientRegistration metadata discovery.

For example:
JwtDecoder OidcConfigurationProvider.issuer()

The returned JwtDecoder would be configured with the jwks_uri from the discovered Provider Configuration and than supplied to resourceServer().jwt().decoder(jwtDecoder).

NOTE: We may have to re-factor the existing OidcConfigurationProvider to support both configurations of ClientRegistration and JwtDecoder. However, we're also debating on keeping these in separate classes - client and resource server specific configs. It's difficult to tell at this point until the work get's started so any suggestions you have let's start that dialogue in a PR.

[rwinch]

and than supplied to resourceServer().jwt().decoder(jwtDecoder).

Spring Security would not configure on the DSL. User's (and Boot) could create a JwtDecoder Bean using the factory and then it would be used by the DSL by default. Alternatively, user's would be able to explicitly inject it via the decoder(..) method

[jgrandja]

Related #5584