Session provider classes are a bit tricky to move to a namespace, as just moving them and updating ext.json references will result in T292779: Account problems (Wrong provider ..\CentralAuth\Session\CentralAuthSessionProvider !== CentralAuthSessionProvider).

There are essentially two options that we have:

• Add support in core for alternative/old names for session providers and use them
• (Permanently) override SessionProvider::__toString() in CA providers

The second one is a bit hacky but needs less effort. I don't really have a preference between those two, feedback appreciated.