OAuth provider base uses magic string that is incompatible with extension conventions.

Extension policy wishes that services be named starting with the vendorname.extension name, however the oAuth provider, which is designed to be extended, uses a magic string in several locations that requires that the service begin with "auth.provider.oauth".

This is either a bug in the oAuth provider or a bug in the EPV not recognizing an intended exception if this naming standard difference was intentional. Examples of the magic string can be found in phpbb/auth/provider/oauth/oauth.php:433 (the service name that is built to look up) or in https://github.com/phpbb/phpbb/blob/6322970766bd9fa78327fa2ca6a6a43d73b680ee/phpBB/phpbb/auth/provider_collection.php#L53.