Would it be possible to request a change to the org.keycloak.adapters.springsecurity.filter.KeycloakAuthenticationProcessingFilter so that it allows providing a different DEFAULT_LOGIN_URL?  Right now you can change it in your Spring bean config for org.keycloak.adapters.springsecurity.authentication.KeycloakAuthenticationEntryPoint but not for the Processing filter.  So you must extend the class to configure it.  This is just a nice to have and not a blocker.

Jeff