Firebase Auth
Google's authentication service with generous free limits and tight integration across the Firebase ecosystem
Firebase Auth handles email/password, social login, phone auth, and anonymous users with minimal setup. Google gives you 50,000 MAU free for most auth methods, which is five times what Clerk or Auth0 offer. If you are already using Firestore or Cloud Functions, Auth plugs in with a single line of config.
The downside is that Firebase Auth is designed to keep you inside Google’s ecosystem. Using it as a standalone auth service — say, with a Postgres database and a Next.js app on Vercel — is doable but clunky compared to Clerk or Supabase Auth. You also need to build your own login UI, since Firebase only provides a basic drop-in widget (FirebaseUI) that looks dated. For solo founders already committed to Firebase, Auth is the obvious choice. For everyone else, evaluate whether you want that Google dependency.
What's good
- 50,000 monthly active users free — most solo products never hit that ceiling
- Google, Apple, GitHub, and 10+ social providers work out of the box
- Plugs directly into Firestore, Cloud Functions, and other Google Cloud services
Watch out for
- Tied to the Google ecosystem — using Firebase Auth without other Firebase services feels awkward
- Custom UI required — no pre-built login components like Clerk offers
- Migrating user password hashes out of Firebase is possible but painful