Does Firebase Work With Auth0?
You can use Auth0 with Firebase, but you're replacing Firebase Authentication entirely, which requires custom integration work.
Quick Facts
How Firebase Works With Auth0
Firebase and Auth0 don't have native integration because they're competing auth solutions. However, you can use Auth0 as your identity provider and connect it to Firebase by exchanging Auth0 tokens for Firebase custom tokens. The typical flow: user authenticates with Auth0, you call Auth0's tokenEndpoint to get an ID token, then exchange that token for a Firebase custom token using the Firebase Admin SDK, which grants access to Firestore/Realtime Database. This approach works well if you need Auth0's advanced features (enterprise SSO, MFA, fine-grained authorization rules) while keeping Firebase's backend infrastructure. The downside is you're maintaining token exchange logic and losing Firebase Authentication's built-in simplicity. Your Firebase security rules must trust the Auth0 user ID you embed in the custom token. This architecture adds latency to authentication since you're making multiple API calls, and you lose some of Firebase's automatic session management conveniences.
Best Use Cases
Auth0 to Firebase Custom Token Exchange
npm install auth0 firebase-adminimport * as admin from 'firebase-admin';
import { ManagementClient } from 'auth0';
// On your backend after Auth0 login
export async function exchangeAuth0TokenForFirebase(
auth0Token: string
): Promise<string> {
// Verify Auth0 token (done by Auth0 SDK or manually)
const decoded = await admin.auth().verifyIdToken(auth0Token);
// Extract Auth0 user ID
const auth0UserId = decoded.sub;
// Create Firebase custom token
const firebaseCustomToken = await admin
.auth()
.createCustomToken(auth0UserId, {
auth0_id: auth0UserId,
email: decoded.email,
});
return firebaseCustomToken;
}
// On your client
import { getAuth, signInWithCustomToken } from 'firebase/auth';
const response = await fetch('/api/exchange-token', {
method: 'POST',
headers: { 'Authorization': `Bearer ${auth0Token}` },
});
const { firebaseToken } = await response.json();
await signInWithCustomToken(getAuth(), firebaseToken);Known Issues & Gotchas
Firebase Security Rules don't understand Auth0 claims without explicit token mapping
Fix: When creating custom tokens, embed Auth0's user ID in the uid field and any custom claims in the claims object. Validate token signatures server-side before creating custom tokens.
Auth0 tokens expire independently from Firebase sessions, causing auth gaps
Fix: Implement token refresh logic on the client side, refreshing Auth0 tokens before they expire and re-exchanging for fresh Firebase custom tokens every hour or on 401 responses.
Firebase Admin SDK's createCustomToken is slow if called on every request
Fix: Cache the Firebase custom token on the client for its full lifetime (1 hour), only refreshing when it approaches expiration or when Auth0 token is refreshed.
Auth0 free tier has limited token lifetime and refresh token rotation policies
Fix: Plan for paid Auth0 tier if you need longer sessions or need to optimize refresh token handling in production.
Alternatives
- •Firebase Authentication + Auth0 Rules (use Firebase Auth natively, call Auth0 APIs for advanced features via Cloud Functions)
- •Supabase + Auth0 (Supabase has native multi-provider support including Auth0)
- •Cognito + Firestore (AWS native alternative with similar enterprise features to Auth0)
Resources
Related Compatibility Guides
Explore more compatibility guides