Get Started with Firebase Authentication on Android

Connect your app to Firebase

If you haven't already, add Firebase to your Android project.

In your project-level build.gradle file, make sure to include Google's Maven repository in both your buildscript and allprojects sections.

Add Firebase Authentication to your app

Add the dependency for the Firebase Authentication Android library to your module (app-level) Gradle file (usually app/build.gradle):

implementation 'com.google.firebase:firebase-auth:18.1.0'

To use an authentication provider, you need to enable it in the Firebase console. Go to the Sign-in Method page in the Firebase Authentication section to enable Email/Password sign-in and any other identity providers you want for your app.

Check current auth state

Declare an instance of FirebaseAuth.

Java

private FirebaseAuth mAuth;EmailPasswordActivity.java

Kotlin

private lateinit var auth: FirebaseAuthEmailPasswordActivity.kt

In the onCreate() method, initialize the FirebaseAuth instance.

Java

// Initialize Firebase Auth
mAuth = FirebaseAuth.getInstance();EmailPasswordActivity.java

Kotlin

// Initialize Firebase Auth
auth = FirebaseAuth.getInstance()EmailPasswordActivity.kt

When initializing your Activity, check to see if the user is currently signed in.

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);
}EmailPasswordActivity.java

Kotlin

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

Sign up new users

Create a new createAccount method that takes in an email address and password, validates them, and then creates a new user with the [createUserWithEmailAndPassword](/docs/reference/android/com/google/firebase/auth/FirebaseAuth.html#createUserWithEmailAndPassword(java.lang.String, java.lang.String) method.

Java

mAuth.createUserWithEmailAndPassword(email, password)
        .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if (task.isSuccessful()) {
                    // Sign in success, update UI with the signed-in user's information
                    Log.d(TAG, "createUserWithEmail:success");
                    FirebaseUser user = mAuth.getCurrentUser();
                    updateUI(user);
                } else {
                    // If sign in fails, display a message to the user.
                    Log.w(TAG, "createUserWithEmail:failure", task.getException());
                    Toast.makeText(EmailPasswordActivity.this, "Authentication failed.",
                            Toast.LENGTH_SHORT).show();
                    updateUI(null);
                }

                // ...
            }
        });EmailPasswordActivity.java

Kotlin

auth.createUserWithEmailAndPassword(email, password)
        .addOnCompleteListener(this) { task ->
            if (task.isSuccessful) {
                // Sign in success, update UI with the signed-in user's information
                Log.d(TAG, "createUserWithEmail:success")
                val user = auth.currentUser
                updateUI(user)
            } else {
                // If sign in fails, display a message to the user.
                Log.w(TAG, "createUserWithEmail:failure", task.exception)
                Toast.makeText(baseContext, "Authentication failed.",
                        Toast.LENGTH_SHORT).show()
                updateUI(null)
            }

            // ...
        }EmailPasswordActivity.kt

Add a form to register new users with their email and password and call this new method when it is submitted. You can see an example in our quickstart sample.

Sign in existing users

Create a new signIn method which takes in an email address and password, validates them, and then signs a user in with the signInWithEmailAndPassword method.

Java

mAuth.signInWithEmailAndPassword(email, password)
        .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if (task.isSuccessful()) {
                    // Sign in success, update UI with the signed-in user's information
                    Log.d(TAG, "signInWithEmail:success");
                    FirebaseUser user = mAuth.getCurrentUser();
                    updateUI(user);
                } else {
                    // If sign in fails, display a message to the user.
                    Log.w(TAG, "signInWithEmail:failure", task.getException());
                    Toast.makeText(EmailPasswordActivity.this, "Authentication failed.",
                            Toast.LENGTH_SHORT).show();
                    updateUI(null);
                }

                // ...
            }
        });EmailPasswordActivity.java

Kotlin

auth.signInWithEmailAndPassword(email, password)
        .addOnCompleteListener(this) { task ->
            if (task.isSuccessful) {
                // Sign in success, update UI with the signed-in user's information
                Log.d(TAG, "signInWithEmail:success")
                val user = auth.currentUser
                updateUI(user)
            } else {
                // If sign in fails, display a message to the user.
                Log.w(TAG, "signInWithEmail:failure", task.exception)
                Toast.makeText(baseContext, "Authentication failed.",
                        Toast.LENGTH_SHORT).show()
                updateUI(null)
            }

            // ...
        }EmailPasswordActivity.kt

Add a form to sign in users with their email and password and call this new method when it is submitted. You can see an example in our quickstart sample.

Access user information

If a user has signed in successfully you can get their account data at any point with the getCurrentUser method.

Java

FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
if (user != null) {
    // Name, email address, and profile photo Url
    String name = user.getDisplayName();
    String email = user.getEmail();
    Uri photoUrl = user.getPhotoUrl();

    // Check if user's email is verified
    boolean emailVerified = user.isEmailVerified();

    // The user's ID, unique to the Firebase project. Do NOT use this value to
    // authenticate with your backend server, if you have one. Use
    // FirebaseUser.getIdToken() instead.
    String uid = user.getUid();
}MainActivity.java

Kotlin

val user = FirebaseAuth.getInstance().currentUser
user?.let {
    // Name, email address, and profile photo Url
    val name = user.displayName
    val email = user.email
    val photoUrl = user.photoUrl

    // Check if user's email is verified
    val emailVerified = user.isEmailVerified

    // The user's ID, unique to the Firebase project. Do NOT use this value to
    // authenticate with your backend server, if you have one. Use
    // FirebaseUser.getToken() instead.
    val uid = user.uid
}MainActivity.kt

Next Steps

Explore the guides on adding other identity and authentication services: