This adds Google signin and signout authentication to this Brew Crew demo: https://www.youtube.com/watch?v=sfA3NWDBPZ4&list=PL4cUxeGkcC9j--TKIdkb3ISfRbJeJYQwC
One thing to watch out for is that most Google/Firebase/Flutter examples you will see only logout/signout of Firebase using something like this: _auth.signOut(); or FirebaseAuth.instance.signOut();
However, to log out / sign out of Google, you need to use this line too: _googleSignIn.disconnect();
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