Client Initiated Backend Authentication Registration

Currently dynamic registration and sector_identitifier_uri work only for clients that have redirect_uris because that is used to validate the client.

CIBA clients do not necessarily have redirect_uris so adding CIBA clients to a group of clients that share a SIU. There seem to be solutions possible for clients with notification_uris and/or jwks_uris this, too, is currently not in standard OpenId.Registration