firebase-auth-basics

Add an auth block to firebase.json specifying providers like anonymous, emailPassword, and googleSignIn, then run firebase deploy --only auth. Only Google, anonymous, and email/password can be enabled via CLI; other providers require the Firebase Console.

Add the Firebase BoM and firebase-auth dependency in build.gradle.kts, then initialize Firebase.auth in your Activity. Use createUserWithEmailAndPassword for sign-up, signInWithEmailAndPassword for login, and auth.currentUser to check sign-in state.

The error occurs when your app's domain is not in the Firebase project's Authorized Domains list. Add the domain (e.g., localhost) in the Firebase Console or firebase.json, without protocol or port—use localhost, not http://localhost:9090.

Yes, but google_sign_in 7.x requires initialization with a clientId on web or the app hangs. A common workaround is skipping GoogleSignIn initialization on web and using FirebaseAuth's signInWithPopup with GoogleAuthProvider instead.

Use request.auth in security rules: allow read, write: if request.auth != null restricts access to authenticated users. You can also match request.auth.uid against document IDs or owner fields for per-user data isolation.

The crash happens when Auth.auth() is initialized inline before FirebaseApp.configure() runs. Use lazy initialization (lazy var auth = Auth.auth()) or create the auth manager only after Firebase configuration completes.