mod_http_oauth2: Declare additional client registration fields as strings Previously any property not listed in the schema was allowed in any form, which is probably a bit too liberal. Instead, limit extra fields to simple strings, which should still allow localized versions of the various URIs and descriptive properties per RFC 7591 §2.2

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