Connect your app to Firebase
If you haven't already, add Firebase to your Android project.
Add Firebase Authentication to your app
In your module (app-level) Gradle file (usually
<project>/<app-module>/build.gradle.ktsor<project>/<app-module>/build.gradle), add the dependency for the Firebase Authentication library for Android. We recommend using the Firebase Android BoM to control library versioning.dependencies { // Import the BoM for the Firebase platform implementation(platform("com.google.firebase:firebase-bom:33.5.1")) // 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") }By using the Firebase Android 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.
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:23.1.0") }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.
(Optional) Prototype and test with Firebase Local Emulator Suite
Before talking about how your app authenticates users, let's introduce a set of tools you can use to prototype and test Authentication functionality: Firebase Local Emulator Suite. If you're deciding among authentication techniques and providers, trying out different data models with public and private data using Authentication and Firebase Security Rules, or prototyping sign-in UI designs, being able to work locally without deploying live services can be a great idea.
An Authentication emulator is part of the Local Emulator Suite, which enables your app to interact with emulated database content and config, as well as optionally your emulated project resources (functions, other databases, and security rules).
Using the Authentication emulator involves just a few steps:
- Adding a line of code to your app's test config to connect to the emulator.
- From the root of your local project directory, running
firebase emulators:start. - Using the Local Emulator Suite UI for interactive prototyping, or the Authentication emulator REST API for non-interactive testing.
A detailed guide is available at Connect your app to the Authentication emulator. For more information, see the Local Emulator Suite introduction.
Now let's continue with how to authenticate users.
Check current auth state
Declare an instance of
FirebaseAuth.Kotlin+KTX
private lateinit var auth: FirebaseAuth
Java
private FirebaseAuth mAuth;
In the
onCreate()method, initialize theFirebaseAuthinstance.Kotlin+KTX
// Initialize Firebase Auth auth = Firebase.auth
Java
// Initialize Firebase Auth mAuth = FirebaseAuth.getInstance();
When initializing your Activity, check to see if the user is currently signed in.
Kotlin+KTX
public override fun onStart() { super.onStart() // Check if user is signed in (non-null) and update UI accordingly. val currentUser = auth.currentUser if (currentUser != null) { reload() } }Java
@Override public void onStart() { super.onStart(); // Check if user is signed in (non-null) and update UI accordingly. FirebaseUser currentUser = mAuth.getCurrentUser(); if(currentUser != null){ reload(); } }
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
method.
Kotlin+KTX
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)
}
}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);
}
}
});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.
Kotlin+KTX
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)
}
}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);
}
}
});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.
Kotlin+KTX
val user = Firebase.auth.currentUser
user?.let {
// Name, email address, and profile photo Url
val name = it.displayName
val email = it.email
val photoUrl = it.photoUrl
// Check if user's email is verified
val emailVerified = it.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.
val uid = it.uid
}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();
}Next Steps
Explore the guides on adding other identity and authentication services: