Haven't used this but I'll try to help you out. Haven't spent much time looking either so take this for what it's worth.

To be returned by auth it would have to be part of the principal. It looks like it is, and should in fact be included in session.

Anyways it looks like it would have to be part of the principal, because the database lookups to query the full user info would require a key from the principal. And as for keys,

Depending on which user endpoint you use, you can pass either a user ID or a username [so you'll need one of those].

https://developer.x.com/en/docs/x-api/users/lookup/quick-start/user-lookup

Did you remember to configure the provider correctly? Strange it wouldn't return errors if not though~

If you have read all the docs, all the examples, tried minimal reproductions, and don't get an answer here, and then let it cook a couple days and still have nothing, this could be a bug right? Make sure you do all of those things first though, imo. Good luck.