Question: where does uid come from?

Thought there was a lot of good stuff in this repo. I've been looking at this one line for a while and curious how it works. You stopped just short of explaining this in your medium article.

In this line databaseBuilder: (_, uid) => FirestoreDatabase(uid: uid), I understand that FirestoreDatabase takes a named parameter called uid, and that the value for that is coming from (_, uid). What I'm not following is where the uid for (_, uid) is actually created and emitted in the first place.

If you have any insights I would appreciate it.

Thanks!

create_flutter_provider_app/lib/main.dart

Line 34 in 8479c6f

databaseBuilder: (_, uid) => FirestoreDatabase(uid: uid),

I might be wrong, but it seems that it's on the lib/auth_widget_builder.dart which is only called on lib/my_app.dart, meaning, from my understanding, that the only way the uid will update is to reboot the entire app.
I'm waiting for an answer, here, meanwhile I've exhausted every explanation.