You can let your users authenticate with Firebase using their Google Accounts by integrating Google Sign-In into your app. ### AI prompt for AI assistance ***For AI assistance, copy the prompt below into your AI coding agent (like Gemini in Android Studio, Antigravity, Claude Code, Codex, and Cursor).** You can customize the prompt and iterate with your agent. Visit [Firebase agent skills](https://firebase.google.com/docs/ai-assistance/agent-skills.md.txt) for detailed installation info.* ``` Help me use Firebase in my app. 1. Make sure that **Firebase agent skills** are installed and updated. For Claude Code, Codex, or Cursor agents, help me install the Firebase plugin. For other agents, run `npx skills add firebase/agent-skills`. Always try to use **Firebase agent skills** for Firebase-related tasks. 2. Help me set up and use Firebase Authentication with Google Sign-In in my app. ``` ## Before you begin [Video](https://www.youtube.com/watch?v=ELB0W7f_Ib4) 1. If you haven't already, [add Firebase to your Android project](https://firebase.google.com/docs/android/setup.md.txt). 2. In your **module (app-level) Gradle file** (usually `//build.gradle.kts` or `//build.gradle`), add the dependency for the Firebase Authentication library for Android. We recommend using the [Firebase Android BoM](https://firebase.google.com/docs/android/learn-more.md.txt#bom) to control library versioning. Also, as part of setting up Firebase Authentication, you need to add the Credential Manager SDK to your app. ``` dependencies { // Import the BoM for the Firebase platform implementation(platform("com.google.firebase:firebase-bom:35.1.0")) // Add the dependency for the Firebase Authentication library // When using the BoM, you don't specify versions in Firebase library dependencies implementation("com.google.firebase:firebase-auth") // Also add the dependencies for the Credential Manager libraries and specify their versions implementation("androidx.credentials:credentials:1.3.0") implementation("androidx.credentials:credentials-play-services-auth:1.3.0") implementation("com.google.android.libraries.identity.googleid:googleid:1.1.1") } ``` By using the [Firebase Android BoM](https://firebase.google.com/docs/android/learn-more.md.txt#bom), your app will always use compatible versions of Firebase Android libraries. *(Alternative)* Add Firebase library dependencies *without* using the BoM If you choose not to use the Firebase BoM, you must specify each Firebase library version in its dependency line. **Note that if you use *multiple* Firebase libraries in your app, we strongly recommend using the BoM to manage library versions, which ensures that all versions are compatible.** ```groovy dependencies { // Add the dependency for the Firebase Authentication library // When NOT using the BoM, you must specify versions in Firebase library dependencies implementation("com.google.firebase:firebase-auth:25.0.0") // Also add the dependencies for the Credential Manager libraries and specify their versions implementation("androidx.credentials:credentials:1.3.0") implementation("androidx.credentials:credentials-play-services-auth:1.3.0") implementation("com.google.android.libraries.identity.googleid:googleid:1.1.1") } ```
3. Specify your app's SHA-1 fingerprint if you haven't already. 1. In the Firebase console, go to the **Settings** \> [**General** tab](https://console.firebase.google.com/project/_/settings/general/). 2. Scroll down to the **Your apps** card, select your Android app, and add your SHA-1 fingerprint in the **SHA certificate fingerprints** field. See [Authenticating Your Client](https://developers.google.com/android/guides/client-auth) for details on how to get your app's SHA fingerprint. 4. Enable Google as a sign-in provider for your Firebase project: 1. In the Firebase console, go to **Security** \> [**Authentication**](https://console.firebase.google.com/project/_/authentication/). 2. In the **Sign-in method** tab, enable the **Google** sign-in provider. 3. Click **Save**. > [!NOTE] > **Tip:** If you prefer to use the [Firebase CLI](https://firebase.google.com/docs/cli.md.txt), run `firebase init auth` to configure authentication providers, and then run `firebase deploy --only auth` to deploy the changes to your project. 5. Update your Firebase config file. 1. When prompted in the Firebase console, download the updated Firebase config file (`google-services.json`), which now contains the OAuth client information required for Google sign-in. 2. Move this updated config file into your Android Studio project, *replacing* the now-outdated corresponding config file. (See [Add Firebase to your Android project](https://firebase.google.com/docs/android/setup.md.txt#add-config-file).) ## Authenticate with Firebase 1. Integrate Sign in with Google into your app by following the steps in the [Credential Manager documentation](https://developer.android.com/identity/sign-in/credential-manager-siwg). Here are the high-level instructions: 1. Instantiate a Google sign in request using `GetGoogleIdOption`. Then, create the Credential Manager request using `GetCredentialRequest`: ### Kotlin ```kotlin // Instantiate a Google sign-in request val googleIdOption = GetGoogleIdOption.Builder() // Your server's client ID, not your Android client ID. .setServerClientId(getString(R.string.default_web_client_id)) // Only show accounts previously used to sign in. .setFilterByAuthorizedAccounts(true) .build() // Create the Credential Manager request val request = GetCredentialRequest.Builder() .addCredentialOption(googleIdOption) .build() ``` ### Java ```java // Instantiate a Google sign-in request GetGoogleIdOption googleIdOption = new GetGoogleIdOption.Builder() .setFilterByAuthorizedAccounts(true) .setServerClientId(getString(R.string.default_web_client_id)) .build(); // Create the Credential Manager request GetCredentialRequest request = new GetCredentialRequest.Builder() .addCredentialOption(googleIdOption) .build(); ``` In the request above, you must pass your "server" client ID to the `setServerClientId` method. To find the OAuth 2.0 client ID: 1. Open the [**Credentials** page](https://console.cloud.google.com/apis/credentials) in the Google Cloud console. 2. The **Web application** type client ID is your backend server's OAuth 2.0 client ID. 2. Check that after you integrate Sign in with Google, your sign-in activity has code similar to the following: ### Kotlin ```kotlin private fun handleSignIn(credential: Credential) { // Check if credential is of type Google ID if (credential is CustomCredential && credential.type == TYPE_GOOGLE_ID_TOKEN_CREDENTIAL) { // Create Google ID Token val googleIdTokenCredential = GoogleIdTokenCredential.createFrom(credential.data) // Sign in to Firebase with using the token firebaseAuthWithGoogle(googleIdTokenCredential.idToken) } else { Log.w(TAG, "Credential is not of type Google ID!") } } ``` ### Java ```java private void handleSignIn(Credential credential) { // Check if credential is of type Google ID if (credential instanceof CustomCredential customCredential && credential.getType().equals(TYPE_GOOGLE_ID_TOKEN_CREDENTIAL)) { // Create Google ID Token Bundle credentialData = customCredential.getData(); GoogleIdTokenCredential googleIdTokenCredential = GoogleIdTokenCredential.createFrom(credentialData); // Sign in to Firebase with using the token firebaseAuthWithGoogle(googleIdTokenCredential.getIdToken()); } else { Log.w(TAG, "Credential is not of type Google ID!"); } } ``` 2. In your sign-in activity's `onCreate` method, get the shared instance of the `FirebaseAuth` object: ### Kotlin ```kotlin private lateinit var auth: FirebaseAuth // ... // Initialize Firebase Auth auth = Firebase.auth ``` ### Java ```java private FirebaseAuth mAuth; // ... // Initialize Firebase Auth mAuth = FirebaseAuth.getInstance(); ``` 3. When initializing your Activity, check to see if the user is currently signed in: ### Kotlin ```kotlin override fun onStart() { super.onStart() // Check if user is signed in (non-null) and update UI accordingly. val currentUser = auth.currentUser updateUI(currentUser) } ``` ### Java ```java @Override public void onStart() { super.onStart(); // Check if user is signed in (non-null) and update UI accordingly. FirebaseUser currentUser = mAuth.getCurrentUser(); updateUI(currentUser); } ``` 4. Now get the user's Google ID token created in step 1, exchange it for a Firebase credential, and authenticate with Firebase using the Firebase credential: ### Kotlin ```kotlin private fun firebaseAuthWithGoogle(idToken: String) { val credential = GoogleAuthProvider.getCredential(idToken, null) auth.signInWithCredential(credential) .addOnCompleteListener(this) { task -> if (task.isSuccessful) { // Sign in success, update UI with the signed-in user's information Log.d(TAG, "signInWithCredential:success") val user = auth.currentUser updateUI(user) } else { // If sign in fails, display a message to the user Log.w(TAG, "signInWithCredential:failure", task.exception) updateUI(null) } } } ``` ### Java ```java private void firebaseAuthWithGoogle(String idToken) { AuthCredential credential = GoogleAuthProvider.getCredential(idToken, null); mAuth.signInWithCredential(credential) .addOnCompleteListener(this, task -> { if (task.isSuccessful()) { // Sign in success, update UI with the signed-in user's information Log.d(TAG, "signInWithCredential:success"); FirebaseUser user = mAuth.getCurrentUser(); updateUI(user); } else { // If sign in fails, display a message to the user Log.w(TAG, "signInWithCredential:failure", task.getException()); updateUI(null); } }); } ``` If the call to `signInWithCredential` succeeds you can use the `getCurrentUser` method to get the user's account data. ## Next steps After a user signs in for the first time, a new user account is created and linked to the credentials---that is, the user name and password, phone number, or auth provider information---the user signed in with. This new account is stored as part of your Firebase project, and can be used to identify a user across every app in your project, regardless of how the user signs in. - In your apps, you can get the user's basic profile information from the [`FirebaseUser`](https://firebase.google.com/docs/reference/android/com/google/firebase/auth/FirebaseUser.md.txt) object. See [Manage Users](https://firebase.google.com/docs/auth/android/manage-users.md.txt). - In your Firebase Realtime Database and Cloud Storage [Security Rules](https://firebase.google.com/docs/database/security/user-security), you can get the signed-in user's unique user ID from the `auth` variable, and use it to control what data a user can access. You can allow users to sign in to your app using multiple authentication providers by [linking auth provider credentials to an existing user account.](https://firebase.google.com/docs/auth/android/account-linking) To sign out a user, call [`signOut`](https://firebase.google.com/docs/reference/android/com/google/firebase/auth/FirebaseAuth.md.txt#signOut()). You also need to clear the current user credential state from all credential providers, as recommended by [the Credential Manager documentation](https://developer.android.com/identity/sign-in/credential-manager-siwg#handle-sign-out): ### Kotlin ```kotlin private fun signOut() { // Firebase sign out auth.signOut() // When a user signs out, clear the current user credential state from all credential providers. lifecycleScope.launch { try { val clearRequest = ClearCredentialStateRequest() credentialManager.clearCredentialState(clearRequest) updateUI(null) } catch (e: ClearCredentialException) { Log.e(TAG, "Couldn't clear user credentials: ${e.localizedMessage}") } } } ``` ### Java ```java private void signOut() { // Firebase sign out mAuth.signOut(); // When a user signs out, clear the current user credential state from all credential providers. ClearCredentialStateRequest clearRequest = new ClearCredentialStateRequest(); credentialManager.clearCredentialStateAsync( clearRequest, new CancellationSignal(), Executors.newSingleThreadExecutor(), new CredentialManagerCallback<>() { @Override public void onResult(@NonNull Void result) { updateUI(null); } @Override public void onError(@NonNull ClearCredentialException e) { Log.e(TAG, "Couldn't clear user credentials: " + e.getLocalizedMessage()); } }); } ```