Custom RelayState with OpenSamlLogoutRequestResolver

[ghaege]

Describe the bug
RelayState Param with SamlLogoutRequest is ignored.
Instead its replaced with a hardcoded UUID and cannot be customized.

To Reproduce
If we call for example the logout api via: http://logout-host:1234/logout?RelayState=http://app-host:5678
the RelayState Param is never processed.

final class OpenSamlLogoutRequestResolver {
..
    String relayState = UUID.randomUUID().toString();

Expected behavior
RelayState should processed or at least be customizable via

@Bean 
Saml2LogoutRequestResolver logoutRequestResolver(
        RelyingPartyRegistrationResolver registrations) {
    
    OpenSaml4LogoutRequestResolver logoutRequest = 
            new OpenSaml4LogoutRequestResolver(registrations);
    logoutRequest.setRelayStateResolver(this::resolveCustomRelayState);
    
    return logoutRequest;
}

Solution
The solution should be very similar to #11065

[jzheaux]

Sounds great, @ghaege. Can you provide a PR that adds the feature?

[ghaege]

yes, but it might take a couple days