React Native Academy · レッスン

Firebaseによるメール認証と電話番号認証

メールアドレスとパスワードによるサインアップ・サインインを実装し、SMS OTPを使った電話番号認証を追加します。onAuthStateChangedオブザーバーを監視してナビゲーションを制御します。

「Firebaseによるメール認証と電話番号認証」はCoddyKit上の無料React Native Academyレッスンです。これはレッスン2/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはReact Native Academy学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 React Native Academyコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Firebase Auth Overview

Firebase Authentication provides ready-made sign-in flows for email/password, phone OTP, and social providers like Google and Apple. All authentication methods are accessed through the auth() singleton from @react-native-firebase/auth.

Firebase Auth manages tokens, refreshes them automatically, and persists the user session in native storage. The onAuthStateChanged observer is the single source of truth for authentication state in your app — always drive navigation from this callback rather than from individual sign-in function results.

Listening to Auth State Changes

Register an onAuthStateChanged observer early in your app's lifecycle, typically in the root layout component. It fires once with the current user on mount, and again whenever the user signs in or out.

The observer returns an unsubscribe function — always call it in the useEffect cleanup to prevent memory leaks. The observer's user parameter is null when no one is signed in and a FirebaseAuthTypes.User object when authenticated.

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

export function useFirebaseAuth() {
  const [user, setUser] = useState(null);
  const [initializing, setInitializing] = useState(true);

  useEffect(() => {
    const unsubscribe = auth().onAuthStateChanged((user) => {
      setUser(user);
      if (initializing) setInitializing(false);
    });

    return unsubscribe; // auto-cleanup on unmount
  }, []);

  return { user, initializing };
}

Email and Password Sign-Up

To register a new user with email and password, call auth().createUserWithEmailAndPassword(email, password). Firebase validates the email format and enforces the minimum password length (6 characters by default) on the server.

After successful sign-up, Firebase automatically signs in the new user — the onAuthStateChanged observer fires immediately with the new user object. You can then prompt the user to verify their email by calling user.sendEmailVerification().

import auth from '@react-native-firebase/auth';

async function signUpWithEmail(email: string, password: string) {
  try {
    const { user } = await auth().createUserWithEmailAndPassword(email, password);
    await user.sendEmailVerification();
    console.log('Sign-up successful, verification email sent to', email);
  } catch (error: any) {
    if (error.code === 'auth/email-already-in-use') {
      Alert.alert('Error', 'That email address is already in use.');
    } else if (error.code === 'auth/invalid-email') {
      Alert.alert('Error', 'That email address is invalid.');
    }
  }
}

Email and Password Sign-In

Returning users sign in with auth().signInWithEmailAndPassword(email, password). This returns a UserCredential object, but in most cases you do not need to handle the return value — the onAuthStateChanged observer already handles navigation.

Wrap sign-in calls in a try/catch and check the error.code property to display user-friendly messages. Firebase uses error codes like auth/wrong-password and auth/user-not-found that you can map to readable messages.

async function signInWithEmail(email: string, password: string) {
  try {
    await auth().signInWithEmailAndPassword(email, password);
    // onAuthStateChanged will fire and handle navigation
  } catch (error: any) {
    const messages: Record<string, string> = {
      'auth/wrong-password': 'Incorrect password.',
      'auth/user-not-found': 'No account found with this email.',
      'auth/too-many-requests': 'Too many failed attempts. Try again later.',
    };
    Alert.alert('Sign In Failed', messages[error.code] ?? 'An error occurred.');
  }
}

Signing Out

Call auth().signOut() to sign out the current user. This clears the local session and triggers onAuthStateChanged with null. If you are driving navigation from the observer, the app will automatically redirect to the sign-in screen.

Sign out is synchronous in behavior but returns a Promise that resolves when the local session is cleared. You do not need to await it unless you want to confirm completion before performing additional actions.

async function handleSignOut() {
  try {
    await auth().signOut();
    // onAuthStateChanged fires with null, navigator switches to auth stack
  } catch (error) {
    console.error('Sign out error:', error);
  }
}

Phone Authentication Overview

Firebase Phone Authentication works by sending a one-time SMS code to the user's phone number and verifying it. The flow has two steps: (1) call signInWithPhoneNumber to trigger the SMS, and (2) confirm the code the user enters.

On iOS, Firebase may silently verify the phone using APNs silent push notifications, bypassing the manual code entry step for known devices. This requires Push Notification capability in your app. On Android, Firebase uses the Play Integrity API to auto-verify codes on trusted devices.

Step 1: Sending the SMS Code

Call auth().signInWithPhoneNumber(phoneNumber) where phoneNumber is in E.164 format (e.g., +14155552671). The method returns a confirmation object that you store in state to use in the second step.

Show a UI that asks the user to enter the 6-digit code they receive via SMS. Use a numeric TextInput with keyboardType='number-pad' and maxLength={6} for a clean code entry experience.

import auth from '@react-native-firebase/auth';
import { useState } from 'react';

export function PhoneAuthScreen() {
  const [phoneNumber, setPhoneNumber] = useState('');
  const [confirmation, setConfirmation] = useState(null);

  async function sendCode() {
    try {
      const confirm = await auth().signInWithPhoneNumber(phoneNumber);
      setConfirmation(confirm);
      // Now show the code entry screen
    } catch (error) {
      Alert.alert('Error', 'Failed to send verification code.');
    }
  }

  // ...
}

Step 2: Confirming the Code

When the user enters the SMS code, call confirmation.confirm(code). If the code is correct, Firebase signs in the user and onAuthStateChanged fires with the authenticated user. If the code is wrong, the method throws with code auth/invalid-verification-code.

Each confirmation object can only be used once. If the code expires or the user requests a new one, you must call signInWithPhoneNumber again to get a new confirmation object.

async function confirmCode(code: string) {
  try {
    await confirmation.confirm(code);
    // User is now signed in, onAuthStateChanged fires
  } catch (error: any) {
    if (error.code === 'auth/invalid-verification-code') {
      Alert.alert('Error', 'The code you entered is incorrect.');
    } else if (error.code === 'auth/code-expired') {
      Alert.alert('Code Expired', 'Please request a new code.');
      setConfirmation(null); // Reset to phone number entry
    }
  }
}

Updating User Profile

After sign-up, you can update the user's display name and photo URL using auth().currentUser.updateProfile(). This stores the data directly on the Firebase Auth user object, making it available without a separate database query.

However, for rich user profiles (bio, address, etc.), it is better to store additional data in Firestore under a users collection, using the user's UID as the document ID. The Auth profile is for core identity data only.

async function updateUserProfile(displayName: string, photoURL: string) {
  const user = auth().currentUser;
  if (!user) return;

  await user.updateProfile({ displayName, photoURL });
  console.log('Profile updated:', auth().currentUser?.displayName);
}

// Also save extended data to Firestore:
await firestore().collection('users').doc(user.uid).set({
  displayName,
  bio: '',
  createdAt: firestore.FieldValue.serverTimestamp(),
});

Password Reset via Email

If a user forgets their password, call auth().sendPasswordResetEmail(email). Firebase sends an email with a link to reset their password. The link opens a Firebase-hosted web page where the user can enter a new password.

This flow does not require any additional native setup. The link is not a deep link into your app — it goes to Firebase's hosted page. If you want the reset flow to open inside your app, configure the Action URL in Firebase Authentication settings to point to your app's domain with dynamic links.

async function sendPasswordReset(email: string) {
  try {
    await auth().sendPasswordResetEmail(email);
    Alert.alert(
      'Email Sent',
      'Check your inbox for a link to reset your password.'
    );
  } catch (error: any) {
    if (error.code === 'auth/user-not-found') {
      // For security, show the same message even if the email is not found
      Alert.alert('Email Sent', 'If this email is registered, you will receive a reset link.');
    }
  }
}

Checking Email Verification Status

After sign-up with email/password, you may want to prevent access to the main app until the user verifies their email. Check auth().currentUser?.emailVerified inside onAuthStateChanged.

Note that emailVerified is not updated in real time — the user must reload the token for the value to reflect verification. Call auth().currentUser?.reload() and then re-read the property after the user claims to have clicked the verification link.

async function checkEmailVerification() {
  const user = auth().currentUser;
  if (!user) return;

  await user.reload(); // Refresh the user object
  if (user.emailVerified) {
    console.log('Email is verified — grant access');
    navigation.replace('Main');
  } else {
    Alert.alert(
      'Not Verified',
      'Please click the link in your email. Tap Resend to get a new link.',
      [
        { text: 'Resend', onPress: () => user.sendEmailVerification() },
        { text: 'OK' },
      ]
    );
  }
}

Quick Check

Test your understanding of React Native Mobile Development concepts from this lesson.

Lesson Recap

In this lesson you learned: how to implement email/password sign-up and sign-in with Firebase Auth, the two-step phone OTP authentication flow using signInWithPhoneNumber and confirmation.confirm, and how to manage user profile updates and email verification. Next up we read and write documents in Cloud Firestore.

よくある質問

「Firebaseによるメール認証と電話番号認証」レッスンは無料ですか？

はい。「Firebaseによるメール認証と電話番号認証」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、React Native Academyコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 React Native Academyコースには全4レッスンが含まれています。

「Firebaseによるメール認証と電話番号認証」で何を学びますか？

メールアドレスとパスワードによるサインアップ・サインインを実装し、SMS OTPを使った電話番号認証を追加します。onAuthStateChangedオブザーバーを監視してナビゲーションを制御します。ブラウザで直接実行するハンズオンコードでReact Native Academyを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

React Native Academyを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのReact Native Academyは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/4です。

「Firebaseによるメール認証と電話番号認証」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このReact Native Academyレッスンでコードを書いて実行できますか？

はい。すべてのReact Native Academyレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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