You can use Firebase Authentication to sign in a user by sending an SMS message to the user's phone. The user signs in using a one-time code contained in the SMS message.
The easiest way to add phone number sign-in to your app is to use FirebaseUI, which includes a drop-in sign-in widget that implements sign-in flows for phone number sign-in, as well as password-based and federated sign-in. This document describes how to implement a phone number sign-in flow using the Firebase SDK.
Before you begin
- If you haven't already, add Firebase to your Android project.
- In your project-level
build.gradlefile, make sure to include Google's Maven repository in both yourbuildscriptandallprojectssections. - Add the dependency for the Firebase Authentication Android library to your
module (app-level) Gradle file (usually
app/build.gradle):implementation 'com.google.firebase:firebase-auth:19.0.0'
- If you haven't yet connected your app to your Firebase project, do so from the Firebase console.
- 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.
Also, note that phone number sign-in requires a physical device and won't work on an emulator.
Security concerns
Authentication using only a phone number, while convenient, is less secure than the other available methods, because possession of a phone number can be easily transferred between users. Also, on devices with multiple user profiles, any user that can receive SMS messages can sign in to an account using the device's phone number.
If you use phone number based sign-in in your app, you should offer it alongside more secure sign-in methods, and inform users of the security tradeoffs 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-in method for your Firebase project:
- In the Firebase console, open the Authentication section.
- On the Sign-in Method page, enable the Phone Number sign-in method.
Firebase's phone number sign-in request quota is high enough that most apps won't be affected. However, if you need to sign in a very high volume of users with phone authentication, you might need to upgrade your pricing plan. See the pricing page.
Send a verification code to the user's phone
To initiate phone number sign-in, present the user an interface that prompts them to type their phone number. Legal requirements vary, but as a best practice and to set expectations for your users, you should inform them that if they use phone sign-in, they might receive an SMS message for verification and standard rates apply.
Then, pass their phone number to the
PhoneAuthProvider.verifyPhoneNumber method to request that Firebase
verify the user's phone number. For example:
Java
PhoneAuthProvider.getInstance().verifyPhoneNumber(
phoneNumber, // Phone number to verify
60, // Timeout duration
TimeUnit.SECONDS, // Unit of timeout
this, // Activity (for callback binding)
mCallbacks); // OnVerificationStateChangedCallbacks
Kotlin
PhoneAuthProvider.getInstance().verifyPhoneNumber(
phoneNumber, // Phone number to verify
60, // Timeout duration
TimeUnit.SECONDS, // Unit of timeout
this, // Activity (for callback binding)
callbacks) // OnVerificationStateChangedCallbacks
The verifyPhoneNumber method is reentrant: if you call it
multiple times, such as in an activity's onStart method, the
verifyPhoneNumber method will not send a second SMS unless the
original request has timed out.
You can use this behavior to resume the phone number sign in process if your
app closes before the user can sign in (for example, while the user is using
their SMS app). After you call verifyPhoneNumber, set a flag that
indicates verification is in progress. Then, save the flag in your Activity's
onSaveInstanceState method and restore the flag in
onRestoreInstanceState. Finally, in your Activity's
onStart method, check if verification is already in progress, and
if so, call verifyPhoneNumber again. Be sure to clear the flag when
verification 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 callbacks
will be auto-detached when the Activity stops, so you can freely write UI
transition code in the callback methods.
The SMS message sent by Firebase can also be localized by specifying the
auth language via the setLanguageCode method on your Auth
instance.
Java
auth.setLanguageCode("fr");
// To apply the default app language instead of explicitly setting it.
// auth.useAppLanguage();
Kotlin
auth.setLanguageCode("fr")
// To apply the default app language instead of explicitly setting it.
// auth.useAppLanguage()
When you call PhoneAuthProvider.verifyPhoneNumber, you must also
provide an instance of OnVerificationStateChangedCallbacks, which
contains implementations of the callback functions that handle the results of
the request. For example:
Java
mCallbacks = new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
@Override
public void onVerificationCompleted(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(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
// ...
}
// 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;
// ...
}
};
Kotlin
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:$credential")
signInWithPhoneAuthCredential(credential)
}
override fun onVerificationFailed(e: FirebaseException) {
// This callback is invoked in an invalid request for verification is made,
// for instance if the the phone number format is not valid.
Log.w(TAG, "onVerificationFailed", e)
if (e is FirebaseAuthInvalidCredentialsException) {
// Invalid request
// ...
} else if (e is FirebaseTooManyRequestsException) {
// The SMS quota for the project has been exceeded
// ...
}
// Show a message and update the UI
// ...
}
override fun onCodeSent(
verificationId: String,
token: PhoneAuthProvider.ForceResendingToken
) {
// The SMS verification code has been sent to the provided phone number, we
// now need to ask the user to enter the code and then construct a credential
// by combining the code with a verification ID.
Log.d(TAG, "onCodeSent:$verificationId")
// Save verification ID and resending token so we can use them latevr
storedVerificationId = verificationId
resendToken = token
// ...
}
}
Verification callbacks
In most apps, you implement the onVerificationCompleted,
onVerificationFailed, and onCodeSent callbacks. You
might also implement onCodeAutoRetrievalTimeOut, depending on your
app'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.)
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's
phone, create a PhoneAuthCredential object, using the verification
code and the verification ID that was passed to the onCodeSent or
onCodeAutoRetrievalTimeOut callback. (When
onVerificationCompleted is called, you get a
PhoneAuthCredential object directly, so you can skip this step.)
To create the PhoneAuthCredential object, call
PhoneAuthProvider.getCredential:
Java
PhoneAuthCredential credential = PhoneAuthProvider.getCredential(verificationId, code);
Kotlin
val credential = PhoneAuthProvider.getCredential(verificationId!!, code)
Sign in the user
After you get a PhoneAuthCredential object, whether in the
onVerificationCompleted callback or by calling
PhoneAuthProvider.getCredential, complete the sign-in flow by
passing the PhoneAuthCredential object to
FirebaseAuth.signInWithCredential:
Java
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();
// ...
} 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
}
}
}
});
}
Kotlin
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
}
}
}
}
Test with whitelisted phone numbers
You can whitelist phone numbers for development via the Firebase console. Whitelisting phone numbers 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.
Phone numbers to whitelist must meet these requirements:
- Make sure you use fictional numbers that do not already exist. Firebase Authentication does not allow you to whitelist existing phone numbers used by real users. One option is to use 555 prefixed numbers as US test phone numbers, for example: +1 650-555-3434
- 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.
- You can add up to 10 phone numbers for development.
- Use test phone numbers/codes that are hard to guess and change those frequently.
Whitelist phone numbers and verification codes
- In the Firebase console, open the Authentication section.
- In the Sign in method tab, enable the Phone provider if you haven't already.
- Open the Phone numbers for testing accordion menu.
- Provide the phone number you want to test, for example: +1 650-555-3434.
- Provide the 6-digit verification code for that specific number, for example: 654321.
- 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 whitelisted phone number in your application. This allows you to perform 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 Services installed.
When you provide the whitelisted phone number and send the verification code, no actual SMS is sent. Instead, you need to provide the previously configured verification code to complete the sign in.
On sign-in completion, a Firebase user is created with that phone number. The user 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 custom claims on these users to differentiate them as fake users if you want to further restrict access.
Integration testing
In addition to manual testing, Firebase Authentication provides APIs to help write integration tests for phone auth testing. These APIs disable app verification by disabling the reCAPTCHA requirement in web and silent push notifications in iOS. This makes automation testing possible in these flows and easier to implement. In addition, they help provide the ability to test instant verification flows on Android.
On Android you can readily use your whitelisted phone numbers without any additional API calls.
Calling verifyPhoneNumber with a whitelisted number triggers the
onCodeSent callback, in which you'll need to provide the corresponding verification
code. This allows testing in Android Emulators.
Java
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.
PhoneAuthProvider.getInstance().verifyPhoneNumber(
phoneNum, 30L /*timeout*/, TimeUnit.SECONDS,
this, new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
@Override
public void onCodeSent(String verificationId,
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(PhoneAuthCredential phoneAuthCredential) {
// Sign in with the credential
// ...
}
@Override
public void onVerificationFailed(FirebaseException e) {
// ...
}
});
Kotlin
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.
PhoneAuthProvider.getInstance().verifyPhoneNumber(
phoneNum, 30L /*timeout*/, TimeUnit.SECONDS,
this, 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.
this@MainActivity.enableUserManuallyInputCode()
}
override fun onVerificationCompleted(phoneAuthCredential: PhoneAuthCredential) {
// Sign in with the credential
// ...
}
override fun onVerificationFailed(e: FirebaseException) {
// ...
}
})
Additionally, you can test auto-retrieval flows in Android by setting the whitelisted number and
its corresponding verification code for auto-retrieval by calling
setAutoRetrievedSmsCodeForPhoneNumber.
When verifyPhoneNumber is
called, it triggers onVerificationCompleted with the PhoneAuthCredential
directly. This works only with whitelisted phone numbers.
Make sure this is disabled and no whitelisted phone numbers are hardcoded in your app when publishing your application to the Google Play store.
Java
// 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);
PhoneAuthProvider phoneAuthProvider = PhoneAuthProvider.getInstance();
phoneAuthProvider.verifyPhoneNumber(
phoneNumber,
60L,
TimeUnit.SECONDS,
this, /* activity */
new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
@Override
public void onVerificationCompleted(PhoneAuthCredential credential) {
// Instant verification is applied and a credential is directly returned.
// ...
}
// ...
});
Kotlin
// The test phone number and code should be whitelisted in the console.
val phoneNumber = "+16505554567"
val smsCode = "123456"
val firebaseAuth = FirebaseAuth.getInstance()
val firebaseAuthSettings = firebaseAuth.firebaseAuthSettings
// Configure faking the auto-retrieval with the whitelisted numbers.
firebaseAuthSettings.setAutoRetrievedSmsCodeForPhoneNumber(phoneNumber, smsCode)
val phoneAuthProvider = PhoneAuthProvider.getInstance()
phoneAuthProvider.verifyPhoneNumber(
phoneNumber,
60L,
TimeUnit.SECONDS,
this, /* activity */
object : PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
override fun onVerificationCompleted(credential: PhoneAuthCredential) {
// Instant verification is applied and a credential is directly returned.
// ...
}
// ...
})
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
FirebaseUserobject. 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
authvariable, 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:
Java
FirebaseAuth.getInstance().signOut();
Kotlin
FirebaseAuth.getInstance().signOut()