We want to do various permission checks during autocreation (e.g. maybe the user's IP is blocked but they have the ipblock-exempt right as global sysops?), but there doesn't exist any good mechanism in MediaWiki to do this, since the local account doesn't exist yet.
Some options:
- Just support anonymous User objects with a name set (e.g. CentralAuth checks $user->isRegistered() before giving it any rights, it would instead check $user->isRegistered() || $user->isItemLoaded( 'name' )). Simple but scary.
- Create a new hook, or maybe a service similar to CentralIdLookup, which takes a username and tells if that username has any global rights. It would be the caller's responsibility to ensure that the user is authenticated with the given central ID. The autocreation logic would probably be the only caller ever so this feels like overkill.