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.