Firebase Authentication

Dependency Add

In your module (app-level) Gradle file (/build.gradle), add the dependency for the Firebase Authentication Android library.

dependencies {
    // Import the BoM for the Firebase platform
    implementation platform('com.google.firebase:firebase-bom:31.2.0')

    //When using the BoM, you don't specify versions
    implementation 'com.google.firebase:firebase-auth-ktx'

    // [START gradle_firebase_ui_auth]
    implementation "com.firebaseui:firebase-ui-auth:8.0.2"

    // Required only if Facebook login support is required
    // Find the latest Facebook SDK releases here: https://goo.gl/Ce5L94
    implementation "com.facebook.android:facebook-android-sdk:4.42.0"

    //Google Play services library and specify its version
    implementation 'com.google.android.gms:play-services-auth:20.4.1'
}

Authentication Services

01. Sign-in providers: In the Firebase console, open the Authentication section enabling your first sign-in method

02. If you support Google Sign-in and haven’t yet specified your app’s SHA-1 fingerprint, do so from the Settings page of the Firebase console. See Authenticating Your Client for details on how to get your app’s SHA-1 fingerprint.

You can also get the SHA-1 of your signing certificate using the Gradle signingReport command:

./gradlew signingReport

03. If you support sign-in with Facebook or Twitter, add string resources to strings.xml that specify the identifying information required by each provider:

<resources>
  <!-- Facebook application ID and custom URL scheme (app ID prefixed by 'fb'). -->
  <string name="facebook_application_id" translatable="false">YOUR_APP_ID</string>
  <string name="facebook_login_protocol_scheme" translatable="false">fbYOUR_APP_ID</string>
</resources>

Sign in with EmailPassword

Get Started with Firebase Authentication on Android

snippets-android/EmailPasswordActivity.kt at 067d83afbe16fe078e0b68e511827f8cfcdd6467 ·…

Sign in with Google

Demonstrate Firebase Authentication using a Google ID Token.

• XML Desing

<com.google.android.gms.common.SignInButton
        android:id="@+id/signInBtn"
        android:layout_width="match_parent"
        android:layout_margin="16dp"
        android:layout_gravity="center"
        android:layout_height="wrap_content"/>

• Activity

1) onViewCreated()
2) onStart()
3) updateUI()

Then click

4) signIn()
5) onActivityResult()
6) firebaseAuthWithGoogle()
7) updateUI()

After SignIn

1)onViewCreated()
2)onStart()
3)updateUI()

[START declare_auth]
private lateinit var auth: FirebaseAuth

private lateinit var googleSignInClient: GoogleSignInClient

companion object {
    private const val TAG = "GoogleActivity"
    private const val RC_SIGN_IN = 9001
}

[START config_signin]

You must pass your “server” client ID to the Credentials page. To find the OAuth 2.0 client ID: The Web application type client ID is your backend server’s OAuth 2.0 client ID

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

    binding.signInBtn.setOnClickListener {
        signIn()
    }
    // Configure Google Sign In
    val gso = GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
        .requestIdToken(getString(R.string.default_web_client_id))
        .requestEmail()
        .build()

    googleSignInClient = activity?.let { GoogleSignIn.getClient(it, gso) }!!
    
    // Initialize Firebase Auth
    auth = Firebase.auth

}

[START on_start_check_user]

override fun onStart() {
    super.onStart()
    // Check if user is signed in (non-null) and update UI accordingly.
    val currentUser = auth.currentUser
    updateUI(currentUser)
}

private fun updateUI(user: FirebaseUser?) {
    if(user!=null) {
        Toast.makeText(context,"ok",Toast.LENGTH_LONG).show()
        activity?.let { Navigation.findNavController(it, R.id.fragmentContainerView) }
            ?.navigate(R.id.homeFragment)
    }
}

[START signin]

private fun signIn() {
    val signInIntent = googleSignInClient.signInIntent

    /*01.The new way (Kotlin)*/
    resultLauncher.launch(signInIntent)
    
    /*02.The old way*/
    startActivityForResult(signInIntent, RC_SIGN_IN)
}

[START onactivityresult]

/* 01. The new way (Kotlin) */
private var resultLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
    if (result.resultCode == Activity.RESULT_OK) {
        // There are no request codes

        val task = GoogleSignIn.getSignedInAccountFromIntent(result.data)
        try {
            // Google Sign In was successful, authenticate with Firebase
            val account = task.getResult(ApiException::class.java)!!
            Log.d(TAG, "firebaseAuthWithGoogle:" + account.id)
            firebaseAuthWithGoogle(account.idToken!!)
        } catch (e: ApiException) {
            // Google Sign In failed, update UI appropriately
            Log.w(TAG, "Google sign in failed", e)
        }
    }
}

/* 02.The old way:*/

override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
    super.onActivityResult(requestCode, resultCode, data)

    // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
    if (requestCode == RC_SIGN_IN) {
        val task = GoogleSignIn.getSignedInAccountFromIntent(data)
        try {
            // Google Sign In was successful, authenticate with Firebase
            val account = task.getResult(ApiException::class.java)!!
            Log.d(TAG, "firebaseAuthWithGoogle:" + account.id)
            firebaseAuthWithGoogle(account.idToken!!)
        } catch (e: ApiException) {
            // Google Sign In failed, update UI appropriately
            Log.w(TAG, "Google sign in failed", e)
        }
    }
}

[START auth_with_google]

/* recommendated */
/*coroutines (Background Thread)*/

private fun firebaseAuthWithGoogle(idToken: String) {
    val credential = GoogleAuthProvider.getCredential(idToken, null)
    GlobalScope.launch(Dispatchers.IO){
        auth.signInWithCredential(credential).await()
        val user = auth.currentUser
        withContext(Dispatchers.Main){
            updateUI(user)
        }
    }
}

/* OR Not-Recommendated
(Main Thread)*/

private fun firebaseAuthWithGoogle(idToken: String) {
    activity?.let {
        auth.signInWithCredential(credential)
            .addOnCompleteListener(it) { 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)
                }
            }
    }
}

Use the Firebase Authentication SDK to sign in the user and obtain the id_token. Below is a simplified example using Firebase Authentication

// Import necessary Firebase libraries
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

// ...

// Create an instance of FirebaseAuth
FirebaseAuth mAuth = FirebaseAuth.getInstance();

// Start the Google Sign-In intent
private void signInWithGoogle() {
    // Implement your Google Sign-In logic here
    // ...

    // After successful sign-in, get the user's ID token
    FirebaseUser currentUser = mAuth.getCurrentUser();
    if (currentUser != null) {
        currentUser.getIdToken(true)
            .addOnCompleteListener(task -> {
                if (task.isSuccessful()) {
                    // Get the ID token
                    String idToken = task.getResult().getToken();
                    // Use the idToken as needed (e.g., pass it to your server)
                    // ...
                } else {
                    // Handle the exception
                    Exception exception = task.getException();
                    exception.printStackTrace();
                }
            });
    }
}

Ref

snippets-android/auth/app/src/main/java/com/google/firebase/quickstart/auth/kotlin at…