Connect your app to Firebase

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

AddFirebase Authentication to your app

1. In yourmodule (app-level) Gradle file(usually<project>/<app-module>/build.gradle.kts or<project>/<app-module>/build.gradle),add the dependency for theFirebase Authentication library for Android. We recommend using theFirebase Android BoMto control library versioning.

   dependencies{// Import theBoM for the Firebase platformimplementation(platform("com.google.firebase:firebase-bom:34.9.0"))// Add the dependency for theFirebase Authentication library// When using theBoM, you don't specify versions in Firebase library dependenciesimplementation("com.google.firebase:firebase-auth")}

   By using theFirebase Android BoM, your app will always use compatible versions of Firebase Android libraries.

   (Alternative)  Add Firebase library dependencies without using theBoM

   If you choose not to use theFirebase BoM, you must specify each Firebase library version in its dependency line.

   Note that if you usemultiple Firebase libraries in your app, we strongly recommend using theBoM to manage library versions, which ensures that all versions are compatible.

   dependencies{// Add the dependency for theFirebase Authentication library// When NOT using theBoM, you must specify versions in Firebase library dependenciesimplementation("com.google.firebase:firebase-auth:24.0.1")}

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

(Optional) Prototype and test withFirebase Local Emulator Suite

Before talking about how your app authenticates users, let's introduce a set oftools you can use to prototype and testAuthentication functionality:Firebase Local Emulator Suite. If you're deciding among authentication techniquesand providers, trying out different data models with public and private datausingAuthentication andFirebase Security Rules, or prototyping sign-in UI designs, being able towork locally without deploying live services can be a great idea.

AnAuthentication emulator is part of theLocal Emulator Suite, whichenables your app to interact with emulated database content and config, aswell as optionally your emulated project resources (functions, other databases,and security rules).

Using theAuthentication emulator involves just a few steps:

1. Adding a line of code to your app's test config to connect to the emulator.
2. From the root of your local project directory, runningfirebase emulators:start.
3. Using theLocal Emulator Suite UI for interactive prototyping, or theAuthentication emulator REST API for non-interactive testing.

A detailed guide is available atConnect your app to theAuthentication emulator.For more information, see theLocal Emulator Suite introduction.

Now let's continue with how to authenticate users.

Check current auth state

1. Declare an instance ofFirebaseAuth.

   Kotlin

   privatelateinitvarauth:FirebaseAuth
   EmailPasswordActivity.kt

   Java

   privateFirebaseAuthmAuth;
   EmailPasswordActivity.java

2. In theonCreate() method, initialize theFirebaseAuth instance.

   Kotlin

   // Initialize Firebase Authauth=Firebase.auth
   EmailPasswordActivity.kt

   Java

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

3. When initializing your Activity, check to see if the user is currently signedin.

   Kotlin

   publicoverridefunonStart(){super.onStart()// Check if user is signed in (non-null) and update UI accordingly.valcurrentUser=auth.currentUserif(currentUser!=null){reload()}}
   EmailPasswordActivity.kt

   Java

   @OverridepublicvoidonStart(){super.onStart();// Check if user is signed in (non-null) and update UI accordingly.FirebaseUsercurrentUser=mAuth.getCurrentUser();if(currentUser!=null){reload();}}
   EmailPasswordActivity.java

Sign up new users

Create a newcreateAccount method that takes in an email address and password,validates them, and then creates a new user with thecreateUserWithEmailAndPasswordmethod.

auth.createUserWithEmailAndPassword(email,password).addOnCompleteListener(this){task->if(task.isSuccessful){// Sign in success, update UI with the signed-in user's informationLog.d(TAG,"createUserWithEmail:success")valuser=auth.currentUserupdateUI(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

mAuth.createUserWithEmailAndPassword(email,password).addOnCompleteListener(this,newOnCompleteListener<AuthResult>(){@OverridepublicvoidonComplete(@NonNullTask<AuthResult>task){if(task.isSuccessful()){// Sign in success, update UI with the signed-in user's informationLog.d(TAG,"createUserWithEmail:success");FirebaseUseruser=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

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

Sign in existing users

Create a newsignIn method which takes in an email address and password,validates them, and then signs a user in with thesignInWithEmailAndPassword method.

auth.signInWithEmailAndPassword(email,password).addOnCompleteListener(this){task->if(task.isSuccessful){// Sign in success, update UI with the signed-in user's informationLog.d(TAG,"signInWithEmail:success")valuser=auth.currentUserupdateUI(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

mAuth.signInWithEmailAndPassword(email,password).addOnCompleteListener(this,newOnCompleteListener<AuthResult>(){@OverridepublicvoidonComplete(@NonNullTask<AuthResult>task){if(task.isSuccessful()){// Sign in success, update UI with the signed-in user's informationLog.d(TAG,"signInWithEmail:success");FirebaseUseruser=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

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

Access user information

If a user has signed in successfully you can get their account data atany point with thegetCurrentUser method.

valuser=Firebase.auth.currentUseruser?.let{// Name, email address, and profile photo Urlvalname=it.displayNamevalemail=it.emailvalphotoUrl=it.photoUrl// Check if user's email is verifiedvalemailVerified=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.valuid=it.uid}
MainActivity.kt

FirebaseUseruser=FirebaseAuth.getInstance().getCurrentUser();if(user!=null){// Name, email address, and profile photo UrlStringname=user.getDisplayName();Stringemail=user.getEmail();UriphotoUrl=user.getPhotoUrl();// Check if user's email is verifiedbooleanemailVerified=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.Stringuid=user.getUid();}
MainActivity.java

Next Steps

Explore the guides on adding other identity and authentication services:

• Google Sign-in
• Facebook Login
• Anonymous Authentication