Authenticate with Firebase Anonymously on Android

You can useFirebase Authentication to create and use temporary anonymous accountsto authenticate with Firebase. These temporary anonymous accounts can be used toallow users who haven't yet signed up to your app to work with data protectedby security rules. If an anonymous user decides to sign up to your app, you canlink their sign-in credentials to the anonymousaccount so that they can continue to work with their protected data infuture sessions.

Before you begin

  1. If you haven't already,add Firebase to your Android project.
  2. 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")}
  3. If you haven't yet connected your app to your Firebase project, do so from theFirebase console.
  4. Enable anonymous auth:
    1. In theFirebase console, open theAuth section.
    2. On theSign-in Methods page, enable theAnonymous sign-in method.
    3. Optional: If you've upgraded your project toFirebase Authentication with Identity Platform, you can enable automatic clean-up. When you enable this setting, anonymous accounts older than 30 days will be automatically deleted. In projects with automatic clean-up enabled, anonymous authentication will no longer count toward usage limits or billing quotas. SeeAutomatic clean-up.

Authenticate with Firebase anonymously

When a signed-out user uses an app feature that requires authentication withFirebase, sign in the user anonymously by completing the following steps:

  1. In your activity'sonCreate method, get the shared instance of theFirebaseAuth object:

    Kotlin

    privatelateinitvarauth:FirebaseAuth// ...// Initialize Firebase Authauth=Firebase.auth

    Java

    privateFirebaseAuthmAuth;// ...// Initialize Firebase AuthmAuth=FirebaseAuth.getInstance();
  2. When initializing your Activity, check to see if the user is currently signed in:

    Kotlin

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

    Java

    @OverridepublicvoidonStart(){super.onStart();// Check if user is signed in (non-null) and update UI accordingly.FirebaseUsercurrentUser=mAuth.getCurrentUser();updateUI(currentUser);}
  3. Finally, callsignInAnonymously to sign in as an anonymous user:

    Kotlin

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

    Java

    mAuth.signInAnonymously().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,"signInAnonymously:success");FirebaseUseruser=mAuth.getCurrentUser();updateUI(user);}else{// If sign in fails, display a message to the user.Log.w(TAG,"signInAnonymously:failure",task.getException());Toast.makeText(AnonymousAuthActivity.this,"Authentication failed.",Toast.LENGTH_SHORT).show();updateUI(null);}}});
    If sign-in succeeds you can use thegetCurrentUser method to get the user's account data.
To protect your project from abuse, Firebase limits the number of newemail/password and anonymous sign-ups that your application can have from thesame IP address in a short period of time. You can request and scheduletemporary changes to this quota from theFirebase console.

Convert an anonymous account to a permanent account

When an anonymous user signs up to your app, you might want to allow them tocontinue their work with their new account—for example, you might want tomake the items the user added to their shopping cart before they signed upavailable in their new account's shopping cart. To do so, complete the followingsteps:

  1. When the user signs up, complete the sign-in flow for the user's authentication provider up to, but not including, calling one of theFirebaseAuth.signInWith methods. For example, get the user's Google ID token, Facebook access token, or email address and password.

  2. Get anAuthCredential for the new authentication provider:

    Google Sign-In

    Kotlin

    valcredential=GoogleAuthProvider.getCredential(googleIdToken,null)

    Java

    AuthCredentialcredential=GoogleAuthProvider.getCredential(googleIdToken,null);
    Facebook Login

    Kotlin

    valcredential=FacebookAuthProvider.getCredential(token.token)

    Java

    AuthCredentialcredential=FacebookAuthProvider.getCredential(token.getToken());
    Email-password sign-in

    Kotlin

    valcredential=EmailAuthProvider.getCredential(email,password)

    Java

    AuthCredentialcredential=EmailAuthProvider.getCredential(email,password);

  3. Pass theAuthCredential object to the sign-in user'slinkWithCredential method:

    Kotlin

    auth.currentUser!!.linkWithCredential(credential).addOnCompleteListener(this){task->if(task.isSuccessful){Log.d(TAG,"linkWithCredential:success")valuser=task.result?.userupdateUI(user)}else{Log.w(TAG,"linkWithCredential:failure",task.exception)Toast.makeText(baseContext,"Authentication failed.",Toast.LENGTH_SHORT,).show()updateUI(null)}}

    Java

    mAuth.getCurrentUser().linkWithCredential(credential).addOnCompleteListener(this,newOnCompleteListener<AuthResult>(){@OverridepublicvoidonComplete(@NonNullTask<AuthResult>task){if(task.isSuccessful()){Log.d(TAG,"linkWithCredential:success");FirebaseUseruser=task.getResult().getUser();updateUI(user);}else{Log.w(TAG,"linkWithCredential:failure",task.getException());Toast.makeText(AnonymousAuthActivity.this,"Authentication failed.",Toast.LENGTH_SHORT).show();updateUI(null);}}});

If the call tolinkWithCredential succeeds, the user's new account canaccess the anonymous account's Firebase data.

This technique can also be used tolink any two accounts.

Automatic clean-up

If you've upgraded your project toFirebase Authentication with Identity Platform, you can enable automatic clean-up in theFirebase console. When you enable this feature you allow Firebase to automatically delete anonymous accounts older than 30 days. In projects with automatic clean-up enabled, anonymous authentication will not count toward usage limits or billing quotas.

  • Any anonymous accounts created after enabling automatic clean-up might be automatically deleted any time after 30 days post-creation.
  • Existing anonymous accounts will be eligible for automatic deletion 30 days after enabling automatic clean-up.
  • If you turn automatic clean-up off, any anonymous accounts scheduled to be deleted will remain scheduled to be deleted.
  • If you "upgrade" an anonymous account by linking it to any sign-in method, the account will not get automatically deleted.

If you want to see how many users will be affected before you enable this feature, and you'veupgraded your project toFirebase Authentication with Identity Platform, you can filter byis_anon inCloudLogging.

Next steps

Now that users can authenticate with Firebase, you can control their access todata in your Firebase database usingFirebase rules.

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Last updated 2026-02-18 UTC.