mod_http_oauth2: Deduplicate client authentication Since it is always performed by each grant_type_handler, it can now be done earlier before dispatching to them. A note on 4f0ed0e3ad5a: Requiring a client in the password grant broke use without registering a client, e.g. the Snikket Web Portal.

module:depends("cloud_notify_encrypted");
module:depends("cloud_notify_priority_tag");
module:depends("cloud_notify_filters");