You can integrate Firebase Authentication with a custom authentication system by
modifying your authentication server to produce custom signed tokens when a user
successfully signs in. Your app receives this token and uses it to authenticate
with Firebase.
Before you begin
- If you haven't already,
add Firebase to your Android project
.
-
In your
module (app-level) Gradle file
(usually
<project>/<app-module>/build.gradle.kts
or
<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:32.8.1"))
// 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:22.3.1")
}
Looking for a Kotlin-specific library module?
Starting in
October 2023
(Firebase BoM 32.5.0)
, both Kotlin and Java developers can
depend on the main library module (for details, see the
FAQ about this initiative
).
- Get your project's server keys:
- Go to the
Service Accounts
page in your project's settings.
- Click
Generate New Private Key
at the bottom of the
Firebase Admin SDK
section of the
Service Accounts
page.
- The new service account's public/private key pair is automatically
saved on your computer. Copy this file to your authentication server.
Authenticate with Firebase
- In your sign-in activity's
onCreate
method, get the shared
instance of the
FirebaseAuth
object:
Kotlin+KTX
private lateinit var auth: FirebaseAuth
// ...
// Initialize Firebase Auth
auth = Firebase.auth
Java
private FirebaseAuth mAuth;
// ...
// 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
updateUI(currentUser)
}
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);
}
- When users sign in to your app, send their sign-in credentials (for
example, their username and password) to your authentication server. Your
server checks the credentials and returns a
custom token
if they are valid.
- After you receive the custom token from your authentication server, pass
it to
signInWithCustomToken
to sign in the user:
Kotlin+KTX
customToken?.let {
auth.signInWithCustomToken(it)
.addOnCompleteListener(this) { task ->
if (task.isSuccessful) {
// Sign in success, update UI with the signed-in user's information
Log.d(TAG, "signInWithCustomToken:success")
val user = auth.currentUser
updateUI(user)
} else {
// If sign in fails, display a message to the user.
Log.w(TAG, "signInWithCustomToken:failure", task.exception)
Toast.makeText(
baseContext,
"Authentication failed.",
Toast.LENGTH_SHORT,
).show()
updateUI(null)
}
}
}
Java
mAuth.signInWithCustomToken(mCustomToken)
.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, "signInWithCustomToken:success");
FirebaseUser user = mAuth.getCurrentUser();
updateUI(user);
} else {
// If sign in fails, display a message to the user.
Log.w(TAG, "signInWithCustomToken:failure", task.getException());
Toast.makeText(CustomAuthActivity.this, "Authentication failed.",
Toast.LENGTH_SHORT).show();
updateUI(null);
}
}
});
If sign-in succeeds, the
AuthStateListener
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
object. See
Manage Users
.
In your Firebase Realtime Database and Cloud Storage
Security Rules
, 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.
To sign out a user, call
signOut
:
Kotlin+KTX
Firebase.auth.signOut()
Java
FirebaseAuth.getInstance().signOut();