Email and Phone Authentication with Firebase
Implement email/password sign-up and sign-in, add phone number authentication with SMS OTP, and listen to the onAuthStateChanged observer to gate navigation.
Email and Phone Authentication with Firebase is a free React Native Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the React Native Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
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.
Frequently asked questions
Is the “Email and Phone Authentication with Firebase” lesson free?
Yes — the full text of “Email and Phone Authentication with Firebase” is free to read here on the web, and the React Native Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the React Native Academy course, upgrade to CoddyKit PRO.
What will I learn in “Email and Phone Authentication with Firebase”?
Implement email/password sign-up and sign-in, add phone number authentication with SMS OTP, and listen to the onAuthStateChanged observer to gate navigation. You practise React Native Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start React Native Academy?
No prior experience is required. React Native Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Email and Phone Authentication with Firebase” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this React Native Academy lesson?
Yes. Every React Native Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Connecting React Native Firebase to Your Project
- Email and Phone Authentication with Firebase
- Reading and Writing Firestore Documents
- Real-Time Listeners and Offline Persistence