BeginnerFirebase Integration

How do you implement Firebase Authentication in Flutter?

Short Answer

Add the `firebase_auth` package, initialize Firebase in `main()`, then use `FirebaseAuth.instance` to sign users in (email/password, Google, etc.) and listen to `authStateChanges()` to react to login/logout across the app.

After running `flutterfire configure` (which wires up your platform-specific Firebase config files) and calling `Firebase.initializeApp()` before `runApp()`, authentication itself is mostly calling methods on `FirebaseAuth.instance`: `createUserWithEmailAndPassword()`, `signInWithEmailAndPassword()`, or a provider-specific sign-in (e.g. Google Sign-In, which gets an OAuth credential and passes it to `signInWithCredential()`).

The key architectural piece is `FirebaseAuth.instance.authStateChanges()`, a Stream that emits the current `User?` (null when signed out) immediately and on every login/logout. Wrapping your app's root in a `StreamBuilder` on this stream is the standard way to route between a login screen and the main app reactively, without manually tracking auth state yourself.

Code Example

StreamBuilder<User?>(
  stream: FirebaseAuth.instance.authStateChanges(),
  builder: (context, snapshot) {
    if (snapshot.connectionState == ConnectionState.waiting) {
      return const SplashScreen();
    }
    return snapshot.hasData ? const HomeScreen() : const LoginScreen();
  },
)

Common Mistakes

×Calling `Firebase.initializeApp()` after `runApp()` instead of before, causing a race condition on startup.
×Manually polling `FirebaseAuth.instance.currentUser` instead of listening to `authStateChanges()`.

How do you implement Firebase Authentication in Flutter?

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