Authenticate with Firebase on Android using a Phone Number  |  Firebase Authentication (2024)

• Firebase
• Documentation
• Authentication
• Build

You can use Firebase Authentication to sign in a user by sending an SMS messageto the user's phone. The user signs in using a one-time code contained in theSMS message.

The easiest way to add phone number sign-in to your app is to useFirebaseUI,which includes a drop-in sign-in widget that implements sign-in flows for phonenumber sign-in, as well as password-based and federated sign-in. This documentdescribes how to implement a phone number sign-in flow using the Firebase SDK.

Before you begin

1. If you haven't already, add Firebase to your Android project.
2. 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 theFirebase Android BoMto control library versioning.

   dependencies { // Import the BoM for the Firebase platform implementation(platform("com.google.firebase:firebase-bom:33.3.0")) // 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 dependencieswithoutusing 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:23.0.0")}

   Looking for a Kotlin-specific library module? Starting inOctober 2023(Firebase BoM 32.5.0), both Kotlin and Java developers candepend on the main library module (for details, see theFAQ about this initiative).
3. If you haven't yet connected your app to your Firebase project, do so from the Firebase console.
4. If you haven't already set your app's SHA-1 hash in the Firebase console, do so. See Authenticating Your Client for information about finding your app's SHA-1 hash.

Security concerns

Authentication using only a phone number, while convenient, is less securethan the other available methods, because possession of a phone numbercan be easily transferred between users. Also, on devices with multiple userprofiles, any user that can receive SMS messages can sign in to an account usingthe device's phone number.

If you use phone number based sign-in in your app, you should offer italongside more secure sign-in methods, and inform users of the securitytradeoffs of using phone number sign-in.

Enable Phone Number sign-in for your Firebase project

To sign in users by SMS, you must first enable the Phone Number sign-inmethod for your Firebase project:

1. In the Firebase console, open the Authentication section.
2. On the Sign-in Method page, enable the Phone Number sign-in method.

Enable app verification

To use phone number authentication, Firebase must be able to verify thatphone number sign-in requests are coming from your app. There are three waysFirebase Authentication accomplishes this:

• Play Integrity API: If a user has a device with Google Play services installed, and Firebase Authentication can verify the device as legitimate with the Play Integrity API, phone number sign-in can proceed. The Play Integrity API is enabled on a Google-owned project by Firebase Authentication, not on your project. This does not contribute to any Play Integrity API quotas on your project. Play Integrity Support is available with the Authentication SDK v21.2.0+ (Firebase BoM v31.4.0+).

  To use Play Integrity, if you haven't yet specified your app's SHA-256 fingerprint, do so from the Project settings of the Firebase console. Refer to Authenticating Your Client for details on how to get your app's SHA-256 fingerprint.

• reCAPTCHA verification: In the event that Play Integrity cannot be used, such as when a user has a device without Google Play services installed, Firebase Authentication uses a reCAPTCHA verification to complete the phone sign-in flow. The reCAPTCHA challenge can often be completed without the user having to solve anything. Note that this flow requires that a SHA-1 is associated with your application. This flow also requires your API Key to be unrestricted or allowlisted for PROJECT_ID.firebaseapp.com.

  Some scenarios where reCAPTCHA is triggered:

  • If the end-user's device does not have Google Play services installed.
  • If the app is not distributed through Google Play Store (on Authentication SDK v21.2.0+).
  • If the obtained SafetyNet token was not valid (on Authentication SDK versions < v21.2.0).

  When SafetyNet or Play Integrity is used for App verification, the %APP_NAME% field in the SMS template is populated with the app name determined from Google Play Store. In the scenarios where reCAPTCHA is triggered, %APP_NAME% is populated as PROJECT_ID.firebaseapp.com.

You can force the reCAPTCHA verification flow withforceRecaptchaFlowForTestingYou can disable app verification (when using fictional phone numbers) usingsetAppVerificationDisabledForTesting.

Troubleshooting

• "Missing initial state" error when using reCAPTCHA for app verification

  This can occur when the reCAPTCHA flow completes successfully but does not redirect the user back to the native application. If this occurs, the user is redirected to the fallback URL PROJECT_ID.firebaseapp.com/__/auth/handler.On Firefox browsers, opening native app links is disabled by default. If you see the above error on Firefox, follow the steps in Set Firefox for Android to open links in native apps to enable opening app links.

Send a verification code to the user's phone

To initiate phone number sign-in, present the user an interface that promptsthem to type their phone number. Legal requirements vary, but as a best practiceand to set expectations for your users, you should inform them that if they usephone sign-in, they might receive an SMS message for verification and standardrates apply.

Then, pass their phone number to thePhoneAuthProvider.verifyPhoneNumber method to request that Firebaseverify the user's phone number. For example:

val options = PhoneAuthOptions.newBuilder(auth) .setPhoneNumber(phoneNumber) // Phone number to verify .setTimeout(60L, TimeUnit.SECONDS) // Timeout and unit .setActivity(this) // Activity (for callback binding) .setCallbacks(callbacks) // OnVerificationStateChangedCallbacks .build()PhoneAuthProvider.verifyPhoneNumber(options)
PhoneAuthActivity.kt

PhoneAuthOptions options = PhoneAuthOptions.newBuilder(mAuth) .setPhoneNumber(phoneNumber) // Phone number to verify .setTimeout(60L, TimeUnit.SECONDS) // Timeout and unit .setActivity(this) // (optional) Activity for callback binding // If no activity is passed, reCAPTCHA verification can not be used. .setCallbacks(mCallbacks) // OnVerificationStateChangedCallbacks .build(); PhoneAuthProvider.verifyPhoneNumber(options); 
PhoneAuthActivity.java

The verifyPhoneNumber method is reentrant: if you call itmultiple times, such as in an activity's onStart method, theverifyPhoneNumber method will not send a second SMS unless theoriginal request has timed out.

You can use this behavior to resume the phone number sign in process if yourapp closes before the user can sign in (for example, while the user is usingtheir SMS app). After you call verifyPhoneNumber, set a flag thatindicates verification is in progress. Then, save the flag in your Activity'sonSaveInstanceState method and restore the flag inonRestoreInstanceState. Finally, in your Activity'sonStart method, check if verification is already in progress, andif so, call verifyPhoneNumber again. Be sure to clear the flag whenverification completes or fails (see Verification callbacks).

To easily handle screen rotation and other instances of Activity restarts,pass your Activity to the verifyPhoneNumber method. The callbackswill be auto-detached when the Activity stops, so you can freely write UItransition code in the callback methods.

The SMS message sent by Firebase can also be localized by specifying theauth language via the setLanguageCode method on your Authinstance.

auth.setLanguageCode("fr")// To apply the default app language instead of explicitly setting it.// auth.useAppLanguage()
MainActivity.kt

auth.setLanguageCode("fr");// To apply the default app language instead of explicitly setting it.// auth.useAppLanguage();
MainActivity.java

When you call PhoneAuthProvider.verifyPhoneNumber, you must alsoprovide an instance of OnVerificationStateChangedCallbacks, whichcontains implementations of the callback functions that handle the results ofthe request. For example:

callbacks = object : PhoneAuthProvider.OnVerificationStateChangedCallbacks() { override fun onVerificationCompleted(credential: PhoneAuthCredential) { // This callback will be invoked in two situations: // 1 - Instant verification. In some cases the phone number can be instantly // verified without needing to send or enter a verification code. // 2 - Auto-retrieval. On some devices Google Play services can automatically // detect the incoming verification SMS and perform verification without // user action. Log.d(TAG, "onVerificationCompleted:$credential") signInWithPhoneAuthCredential(credential) } override fun onVerificationFailed(e: FirebaseException) { // This callback is invoked in an invalid request for verification is made, // for instance if the the phone number format is not valid. Log.w(TAG, "onVerificationFailed", e) if (e is FirebaseAuthInvalidCredentialsException) { // Invalid request } else if (e is FirebaseTooManyRequestsException) { // The SMS quota for the project has been exceeded } else if (e is FirebaseAuthMissingActivityForRecaptchaException) { // reCAPTCHA verification attempted with null Activity } // Show a message and update the UI } override fun onCodeSent( verificationId: String, token: PhoneAuthProvider.ForceResendingToken, ) { // The SMS verification code has been sent to the provided phone number, we // now need to ask the user to enter the code and then construct a credential // by combining the code with a verification ID. Log.d(TAG, "onCodeSent:$verificationId") // Save verification ID and resending token so we can use them later storedVerificationId = verificationId resendToken = token }}
PhoneAuthActivity.kt

mCallbacks = new PhoneAuthProvider.OnVerificationStateChangedCallbacks() { @Override public void onVerificationCompleted(@NonNull PhoneAuthCredential credential) { // This callback will be invoked in two situations: // 1 - Instant verification. In some cases the phone number can be instantly // verified without needing to send or enter a verification code. // 2 - Auto-retrieval. On some devices Google Play services can automatically // detect the incoming verification SMS and perform verification without // user action. Log.d(TAG, "onVerificationCompleted:" + credential); signInWithPhoneAuthCredential(credential); } @Override public void onVerificationFailed(@NonNull FirebaseException e) { // This callback is invoked in an invalid request for verification is made, // for instance if the the phone number format is not valid. Log.w(TAG, "onVerificationFailed", e); if (e instanceof FirebaseAuthInvalidCredentialsException) { // Invalid request } else if (e instanceof FirebaseTooManyRequestsException) { // The SMS quota for the project has been exceeded } else if (e instanceof FirebaseAuthMissingActivityForRecaptchaException) { // reCAPTCHA verification attempted with null Activity } // Show a message and update the UI } @Override public void onCodeSent(@NonNull String verificationId, @NonNull PhoneAuthProvider.ForceResendingToken token) { // The SMS verification code has been sent to the provided phone number, we // now need to ask the user to enter the code and then construct a credential // by combining the code with a verification ID. Log.d(TAG, "onCodeSent:" + verificationId); // Save verification ID and resending token so we can use them later mVerificationId = verificationId; mResendToken = token; }};
PhoneAuthActivity.java

Verification callbacks

In most apps, you implement the onVerificationCompleted,onVerificationFailed, and onCodeSent callbacks. Youmight also implement onCodeAutoRetrievalTimeOut, depending on yourapp's requirements.

onVerificationCompleted(PhoneAuthCredential)

This method is called in two situations:

• Instant verification: in some cases the phone number can be instantly verified without needing to send or enter a verification code.
• Auto-retrieval: on some devices, Google Play services can automatically detect the incoming verification SMS and perform verification without user action. (This capability might be unavailable with some carriers.) This uses the SMS Retriever API, which includes an 11 character hash at the end of the SMS message.

In either case, the user's phone number has been verified successfully, and you can use the PhoneAuthCredential object that's passed to the callback to sign in the user.

onVerificationFailed(FirebaseException)

This method is called in response to an invalid verification request, such as a request that specifies an invalid phone number or verification code.

onCodeSent(String verificationId, PhoneAuthProvider.ForceResendingToken)

Optional. This method is called after the verification code has been sent by SMS to the provided phone number.

When this method is called, most apps display a UI that prompts the user to type the verification code from the SMS message. (At the same time, auto-verification might be proceeding in the background.) Then, after the user types the verification code, you can use the verification code and the verification ID that was passed to the method to create a PhoneAuthCredential object, which you can in turn use to sign in the user. However, some apps might wait until onCodeAutoRetrievalTimeOut is called before displaying the verification code UI (not recommended).

onCodeAutoRetrievalTimeOut(String verificationId)

Optional. This method is called after the timeout duration specified to verifyPhoneNumber has passed without onVerificationCompleted triggering first. On devices without SIM cards, this method is called immediately because SMS auto-retrieval isn't possible.

Some apps block user input until the auto-verification period has timed out, and only then display a UI that prompts the user to type the verification code from the SMS message (not recommended).

Create a PhoneAuthCredential object

After the user enters the verification code that Firebase sent to the user'sphone, create a PhoneAuthCredential object, using the verificationcode and the verification ID that was passed to the onCodeSent oronCodeAutoRetrievalTimeOut callback. (WhenonVerificationCompleted is called, you get aPhoneAuthCredential object directly, so you can skip this step.)

To create the PhoneAuthCredential object, callPhoneAuthProvider.getCredential:

val credential = PhoneAuthProvider.getCredential(verificationId!!, code)
PhoneAuthActivity.kt

PhoneAuthCredential credential = PhoneAuthProvider.getCredential(verificationId, code);
PhoneAuthActivity.java

Sign in the user

After you get a PhoneAuthCredential object, whether in theonVerificationCompleted callback or by callingPhoneAuthProvider.getCredential, complete the sign-in flow bypassing the PhoneAuthCredential object toFirebaseAuth.signInWithCredential:

private fun signInWithPhoneAuthCredential(credential: PhoneAuthCredential) { auth.signInWithCredential(credential) .addOnCompleteListener(this) { task -> if (task.isSuccessful) { // Sign in success, update UI with the signed-in user's information Log.d(TAG, "signInWithCredential:success") val user = task.result?.user } else { // Sign in failed, display a message and update the UI Log.w(TAG, "signInWithCredential:failure", task.exception) if (task.exception is FirebaseAuthInvalidCredentialsException) { // The verification code entered was invalid } // Update UI } }}
PhoneAuthActivity.kt

private void signInWithPhoneAuthCredential(PhoneAuthCredential credential) { mAuth.signInWithCredential(credential) .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, "signInWithCredential:success"); FirebaseUser user = task.getResult().getUser(); // Update UI } else { // Sign in failed, display a message and update the UI Log.w(TAG, "signInWithCredential:failure", task.getException()); if (task.getException() instanceof FirebaseAuthInvalidCredentialsException) { // The verification code entered was invalid } } } });}
PhoneAuthActivity.java

Test with fictional phone numbers

You can set up fictional phone numbers for development via the Firebase console. Testing with fictional phonenumbers provides these benefits:

• Test phone number authentication without consuming your usage quota.
• Test phone number authentication without sending an actual SMS message.
• Run consecutive tests with the same phone number without getting throttled. This minimizes the risk of rejection during App store review process if the reviewer happens to use the same phone number for testing.
• Test readily in development environments without any additional effort, such as the ability to develop in an iOS simulator or an Android emulator without Google Play Services.
• Write integration tests without being blocked by security checks normally applied on real phone numbers in a production environment.

Fictional phone numbers must meet these requirements:

1. Make sure you use phone numbers that are indeed fictional, and do not already exist. Firebase Authentication does not allow you to set existing phone numbers used by real users as test numbers. One option is to use 555 prefixed numbers as US test phone numbers, for example: +1 650-555-3434
2. Phone numbers have to be correctly formatted for length and other constraints. They will still go through the same validation as a real user's phone number.
3. You can add up to 10 phone numbers for development.
4. Use test phone numbers/codes that are hard to guess and change those frequently.

Create fictional phone numbers and verification codes

1. In the Firebase console, open the Authentication section.
2. In the Sign in method tab, enable the Phone provider if you haven't already.
3. Open the Phone numbers for testing accordion menu.
4. Provide the phone number you want to test, for example: +1 650-555-3434.
5. Provide the 6-digit verification code for that specific number, for example: 654321.
6. Add the number. If there's a need, you can delete the phone number and its code by hovering over the corresponding row and clicking the trash icon.

Manual testing

You can directly start using a fictional phone number in your application. This allows you toperform manual testing during development stages without running into quota issues or throttling.You can also test directly from an iOS simulator or Android emulator without Google Play Servicesinstalled.

When you provide the fictional phone number and send the verification code, no actual SMS issent. Instead, you need to provide the previously configured verification code to complete the signin.

On sign-in completion, a Firebase user is created with that phone number. Theuser has the same behavior and properties as a real phone number user, and can access Realtime Database/Cloud Firestore and other services the same way. The ID token minted during this process has the same signature as a real phone number user.

Another option is to set a test role via customclaims on these users to differentiate them as fake users if you want to further restrictaccess.

To manually trigger the reCAPTCHA flow for testing, use the forceRecaptchaFlowForTesting() method.

// Force reCAPTCHA flowFirebaseAuth.getInstance().getFirebaseAuthSettings().forceRecaptchaFlowForTesting();

Integration testing

In addition to manual testing, Firebase Authentication provides APIs to help write integration testsfor phone auth testing. These APIs disable app verification by disabling the reCAPTCHArequirement in web and silent push notifications in iOS. This makes automation testing possible inthese flows and easier to implement. In addition, they help provide the ability to test instantverification flows on Android.

On Android, call setAppVerificationDisabledForTesting() before the signInWithPhoneNumber call. This disables app verification automatically,allowing you to pass the phone number without manually solving it. Even thoughPlay Integrity and reCAPTCHA are disabled, using a real phone number will still fail tocomplete sign in. Only fictional phone numbers can be used with this API.

// Turn off phone auth app verification.FirebaseAuth.getInstance().getFirebaseAuthSettings() .setAppVerificationDisabledForTesting();

Calling verifyPhoneNumber with a fictional number triggers theonCodeSent callback, in which you'll need to provide the corresponding verificationcode. This allows testing in Android Emulators.

String phoneNum = "+16505554567";String testVerificationCode = "123456";// Whenever verification is triggered with the whitelisted number,// provided it is not set for auto-retrieval, onCodeSent will be triggered.FirebaseAuth auth = FirebaseAuth.getInstance();PhoneAuthOptions options = PhoneAuthOptions.newBuilder(auth) .setPhoneNumber(phoneNum) .setTimeout(60L, TimeUnit.SECONDS) .setActivity(this) .setCallbacks(new PhoneAuthProvider.OnVerificationStateChangedCallbacks() { @Override public void onCodeSent(@NonNull String verificationId, @NonNull PhoneAuthProvider.ForceResendingToken forceResendingToken) { // Save the verification id somewhere // ... // The corresponding whitelisted code above should be used to complete sign-in. MainActivity.this.enableUserManuallyInputCode(); } @Override public void onVerificationCompleted(@NonNull PhoneAuthCredential phoneAuthCredential) { // Sign in with the credential // ... } @Override public void onVerificationFailed(@NonNull FirebaseException e) { // ... } }) .build();PhoneAuthProvider.verifyPhoneNumber(options);
MainActivity.java

val phoneNum = "+16505554567"val testVerificationCode = "123456"// Whenever verification is triggered with the whitelisted number,// provided it is not set for auto-retrieval, onCodeSent will be triggered.val options = PhoneAuthOptions.newBuilder(Firebase.auth) .setPhoneNumber(phoneNum) .setTimeout(30L, TimeUnit.SECONDS) .setActivity(this) .setCallbacks(object : PhoneAuthProvider.OnVerificationStateChangedCallbacks() { override fun onCodeSent( verificationId: String, forceResendingToken: PhoneAuthProvider.ForceResendingToken, ) { // Save the verification id somewhere // ... // The corresponding whitelisted code above should be used to complete sign-in. [email protected]() } override fun onVerificationCompleted(phoneAuthCredential: PhoneAuthCredential) { // Sign in with the credential // ... } override fun onVerificationFailed(e: FirebaseException) { // ... } }) .build()PhoneAuthProvider.verifyPhoneNumber(options)
MainActivity.kt

Additionally, you can test auto-retrieval flows in Android by setting the fictional number andits corresponding verification code for auto-retrieval by callingsetAutoRetrievedSmsCodeForPhoneNumber.

When verifyPhoneNumber iscalled, it triggers onVerificationCompleted with the PhoneAuthCredentialdirectly. This works only with fictional phone numbers.

Make sure this is disabled and no fictional phone numbers are hardcoded inyour app when publishing your application to the Google Play store.

// The test phone number and code should be whitelisted in the console.String phoneNumber = "+16505554567";String smsCode = "123456";FirebaseAuth firebaseAuth = FirebaseAuth.getInstance();FirebaseAuthSettings firebaseAuthSettings = firebaseAuth.getFirebaseAuthSettings();// Configure faking the auto-retrieval with the whitelisted numbers.firebaseAuthSettings.setAutoRetrievedSmsCodeForPhoneNumber(phoneNumber, smsCode);PhoneAuthOptions options = PhoneAuthOptions.newBuilder(firebaseAuth) .setPhoneNumber(phoneNumber) .setTimeout(60L, TimeUnit.SECONDS) .setActivity(this) .setCallbacks(new PhoneAuthProvider.OnVerificationStateChangedCallbacks() { @Override public void onVerificationCompleted(@NonNull PhoneAuthCredential credential) { // Instant verification is applied and a credential is directly returned. // ... } // ... }) .build();PhoneAuthProvider.verifyPhoneNumber(options);
MainActivity.java

// The test phone number and code should be whitelisted in the console.val phoneNumber = "+16505554567"val smsCode = "123456"val firebaseAuth = Firebase.authval firebaseAuthSettings = firebaseAuth.firebaseAuthSettings// Configure faking the auto-retrieval with the whitelisted numbers.firebaseAuthSettings.setAutoRetrievedSmsCodeForPhoneNumber(phoneNumber, smsCode)val options = PhoneAuthOptions.newBuilder(firebaseAuth) .setPhoneNumber(phoneNumber) .setTimeout(60L, TimeUnit.SECONDS) .setActivity(this) .setCallbacks(object : PhoneAuthProvider.OnVerificationStateChangedCallbacks() { override fun onVerificationCompleted(credential: PhoneAuthCredential) { // Instant verification is applied and a credential is directly returned. // ... } // ... }) .build()PhoneAuthProvider.verifyPhoneNumber(options)
MainActivity.kt

Next steps

After a user signs in for the first time, a new user account is created andlinked to the credentials—that is, the user name and password, phonenumber, or auth provider information—the user signed in with. This newaccount is stored as part of your Firebase project, and can be used to identifya 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 theFirebaseUser 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 authenticationproviders by linking auth provider credentials to anexisting user account.

To sign out a user, call signOut:

Firebase.auth.signOut()
MainActivity.kt

FirebaseAuth.getInstance().signOut();
MainActivity.java