Phone authentication allows users to sign in to Firebase using their phone as the authenticator. An SMS message is sent to the user via their phone number containing a unique code. Once the code has been authorized, the user is able to sign in to Firebase.

Phone numbers that end users provide for authentication will be sent and stored by Google to improve our spam and abuse prevention across Google services, including but not limited to Firebase. Developers should ensure they have appropriate end-user consent prior to using the Firebase Authentication phone number sign-in service.

Firebase Phone Auth is not supported in all countries. Please see their FAQs for more information.

Ensure the "Phone" sign-in provider is enabled on the Firebase Console.

iOS Setup

Ensure that all parts of step 1 and 2 from the official firebase iOS phone auth docs have been followed, noting in particular that you may need to re-download your firebase GoogleService-Info.plist file and for the reCAPTCHA flow to work you must make sure you have added your custom URL scheme to your project plist file.

Phone auth requires app verification, and the automatic app verification process uses data-only firebase cloud messages to the app. Data-only cloud messaging only works on real devices where the app has background refresh enabled. If background refresh disabled, or if using the Simulator, app verification uses the fallback reCAPTCHA flow allowing you to check if it is configured correctly.

For reliable automated testing, you may want to disable both automatic and fallback reCAPTCHA app verification for your app. To do this, you may disable app verification in AuthSettings prior to calling any phone auth methods.

Android Setup

Ensure that all parts of step 1 and 2 from the official firebase Android phone auth docs have been followed.

To bypass Play Integrity for manual testing, you may force reCAPTCHA to be used prior to calling verifyPhoneNumber.

Expo Setup

To use phone auth in an expo app, add the @react-native-firebase/auth config plug-in to the plugins section of your app.json. This is in addition to the @react-native-firebase/app plugin.

{
  "expo": {
    "plugins": ["@react-native-firebase/app", "@react-native-firebase/auth"]
  }
}

The @react-native-firebase/auth config plugin is not required for all auth providers, but it is required to use phone auth. The plugin will set up reCAPTCHA verification for you on iOS.

The recommendation is to use a custom development client. For more info on using Expo with React Native Firebase, see our Expo docs.

Sign-in

The module provides a signInWithPhoneNumber method which accepts a phone number. Firebase sends an SMS message to the user with a code, which they must then confirm. The signInWithPhoneNumber method returns a confirmation method which accepts a code. Based on whether the code is correct for the device, the method rejects or resolves.

The example below demonstrates how you could setup such a flow within your own application:

import React, { useState, useEffect } from 'react';
import { Button, TextInput } from 'react-native';
import auth from '@react-native-firebase/auth';

function PhoneSignIn() {
  // If null, no SMS has been sent
  const [confirm, setConfirm] = useState(null);

  // verification code (OTP - One-Time-Passcode)
  const [code, setCode] = useState('');

  // Handle login
  function onAuthStateChanged(user) {
    if (user) {
      // Some Android devices can automatically process the verification code (OTP) message, and the user would NOT need to enter the code.
      // Actually, if he/she tries to enter it, he/she will get an error message because the code was already used in the background.
      // In this function, make sure you hide the component(s) for entering the code and/or navigate away from this screen.
      // It is also recommended to display a message to the user informing him/her that he/she has successfully logged in.
    }
  }

  useEffect(() => {
    const subscriber = auth().onAuthStateChanged(onAuthStateChanged);
    return subscriber; // unsubscribe on unmount
  }, []);

  // Handle the button press
  async function signInWithPhoneNumber(phoneNumber) {
    const confirmation = await auth().signInWithPhoneNumber(phoneNumber);
    setConfirm(confirmation);
  }

  async function confirmCode() {
    try {
      await confirm.confirm(code);
    } catch (error) {
      console.log('Invalid code.');
    }
  }

  if (!confirm) {
    return (
      <Button
        title="Phone Number Sign In"
        onPress={() => signInWithPhoneNumber('+1 650-555-3434')}
      />
    );
  }

  return (
    <>
      <TextInput value={code} onChangeText={text => setCode(text)} />
      <Button title="Confirm Code" onPress={() => confirmCode()} />
    </>
  );
}

Upon successful sign-in, any onAuthStateChanged listeners will trigger with the new authentication state of the user.

Testing

Firebase provides support for locally testing phone numbers. For local testing to work, you must have ensured your local machine SHA1 debug key was added whilst creating your application on the Firebase Console. View the Getting Started guide on how to set this up.

On the Firebase Console, select the "Phone" authentication provider and click on the "Phone numbers for testing" dropdown.

Enter a new phone number (e.g. +44 7444 555666) and a test code (e.g. 123456).

Once added, the number can be used with the signInWithPhoneNumber method, and entering the code specified will cause a successful sign-in.

MFA-like Account Creation

After successfully creating a user with an email and password (see Authentication/Usage/Email/Password sign-in), use the verifyPhoneNumber method to send a verification code to a user's phone number and if the user enters the correct code, link the phone number to the authenticated user's account. This creates a MFA-like authentication flow for account creation. However, to implement MFA with firebase, your app must call additional methods and use Google Cloud Identity Platform, which is a paid service, details available in this guide https://cloud.google.com/identity-platform/docs/web/mfa

import React, { useState, useEffect } from 'react';
import { Button, TextInput, Text } from 'react-native';
import auth from '@react-native-firebase/auth';

export default function PhoneVerification() {
  // Set an initializing state whilst Firebase connects
  const [initializing, setInitializing] = useState(true);
  const [user, setUser] = useState();

  // If null, no SMS has been sent
  const [confirm, setConfirm] = useState(null);

  const [code, setCode] = useState('');

  // Handle user state changes
  function onAuthStateChanged(user) {
    setUser(user);
    if (initializing) setInitializing(false);
  }

  useEffect(() => {
    const subscriber = auth().onAuthStateChanged(onAuthStateChanged);
    return subscriber; // unsubscribe on unmount
  }, []);

  // Handle create account button press
  async function createAccount() {
    try {
      await auth().createUserWithEmailAndPassword('jane.doe@example.com', 'SuperSecretPassword!');
      console.log('User account created & signed in!');
    } catch (error) {
      if (error.code === 'auth/email-already-in-use') {
        console.log('That email address is already in use!');
      }

      if (error.code === 'auth/invalid-email') {
        console.log('That email address is invalid!');
      }
      console.error(error);
    }
  }

  // Handle the verify phone button press
  async function verifyPhoneNumber(phoneNumber) {
    const confirmation = await auth().verifyPhoneNumber(phoneNumber);
    setConfirm(confirmation);
  }

  // Handle confirm code button press
  async function confirmCode() {
    try {
      const credential = auth.PhoneAuthProvider.credential(confirm.verificationId, code);
      let userData = await auth().currentUser.linkWithCredential(credential);
      setUser(userData.user);
    } catch (error) {
      if (error.code == 'auth/invalid-verification-code') {
        console.log('Invalid code.');
      } else {
        console.log('Account linking error');
      }
    }
  }

  if (initializing) return null;

  if (!user) {
    return <Button title="Login" onPress={() => createAccount()} />;
  } else if (!user.phoneNumber) {
    if (!confirm) {
      return (
        <Button
          title="Verify Phone Number"
          onPress={() => verifyPhoneNumber('ENTER A VALID TESTING OR REAL PHONE NUMBER HERE')}
        />
      );
    }
    return (
      <>
        <TextInput value={code} onChangeText={text => setCode(text)} />
        <Button title="Confirm Code" onPress={() => confirmCode()} />
      </>
    );
  } else {
    return (
      <Text>
        Welcome! {user.phoneNumber} linked with {user.email}
      </Text>
    );
  }
}