Updating logged in user does not update widget - flutter

Question

I am building a simple AuthProvider, and based on whether the user is null or not, show either the MainApp or Gatekeeper.
Unfortunately, even though my AuthProvider prints an updated fbUser value, my Widget never updates. What am I doing wrong?
When the firebase authstate changes, I am updating the user value in AuthProvider:
class AuthProvider extends ChangeNotifier {
firebaseAuth.User fbUser;
StreamSubscription _userAuthSub;
AuthProvider() {
_userAuthSub = firebaseAuth.FirebaseAuth.instance
.authStateChanges()
.listen((firebaseAuth.User user) {
if (user == null) {
fbUser = null;
} else {
print('User is signed in!');
fbUser = user;
}
notifyListeners();
});
}
#override
void dispose() {
if (_userAuthSub != null) {
_userAuthSub.cancel();
_userAuthSub = null;
}
super.dispose();
}
Future<firebaseAuth.UserCredential> signInWithGoogle() async {
// Trigger the authentication flow
final GoogleSignInAccount googleUser = await GoogleSignIn().signIn();
// Obtain the auth details from the request
final GoogleSignInAuthentication googleAuth =
await googleUser.authentication;
// Create a new credential
final firebaseAuth.GoogleAuthCredential credential =
firebaseAuth.GoogleAuthProvider.credential(
accessToken: googleAuth.accessToken,
idToken: googleAuth.idToken,
);
// Once signed in, return the UserCredential
return await firebaseAuth.FirebaseAuth.instance
.signInWithCredential(credential);
}
}
Here's my main.dart file, where I use the AuthProvider:
class MeApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MultiProvider(
providers: [
ChangeNotifierProvider<AuthProvider>(
create: (_) => AuthProvider(),
)
],
child: MaterialApp(
home: Scaffold(body: GatekeeperView())));
}
}
And finally here is Gatekeeper consuming this AuthProvider:
class GatekeeperView extends StatelessWidget {
Widget _logo(BuildContext context) {
return Text("LOGO",
style: Theme.of(context)
.textTheme
.headline2
.copyWith(fontWeight: FontWeight.bold));
}
Widget _gatekeeper(BuildContext context) {
final height = MediaQuery.of(context).size.height;
final width = MediaQuery.of(context).size.width;
return Scaffold(
body: Container(
height: height,
alignment: Alignment.center,
padding: EdgeInsets.symmetric(horizontal: 16),
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
_logo(context),
SizedBox(height: height * 0.2),
SizedBox(
width: width * 0.6,
child: FlatButton(
color: Colors.orange,
textColor: Colors.white,
padding: EdgeInsets.all(12),
onPressed: () {
Navigator.pushReplacement(
context,
PageRouteBuilder(
pageBuilder: (c, a1, a2) => LoginView(),
transitionsBuilder: (c, anim, a2, child) =>
FadeTransition(opacity: anim, child: child),
transitionDuration: Duration(milliseconds: 300),
));
},
child: Text("Log In")),
),
],
),
),
);
}
#override
Widget build(BuildContext context) {
return SafeArea(
child: Consumer<AuthProvider>(builder: (context, auth, child) {
if (auth.fbUser != null) {
print("OK"); // <--- this never prints even though the AuthProvider prints "User is signed in"
return Text("Welcome you are logged in");
}
return _gatekeeper(context);
}));
}
}