SuperTokens
Open-source authentication you can self-host for free or use their managed service
SuperTokens is an open-source auth provider that gives you a real alternative to paying per-user fees. Self-host the SuperTokens core (a Java service) alongside your app, and you get email/password, social login, passwordless, session management, and MFA without paying anyone anything. The managed version is free up to 5,000 MAU if you do not want to run infrastructure.
The tradeoff is operational complexity. Self-hosting means you own the auth infrastructure — updates, monitoring, backups. The core service runs on Java, which adds a dependency some teams would rather avoid. If you are building a product where long-term auth costs matter (high user count, thin margins), SuperTokens can save you thousands per year. If you just want auth working in an afternoon and do not mind paying Clerk or Auth0 later, those are faster to set up.
What's good
- Fully open source (Apache 2.0) — inspect every line, fork it, no vendor lock-in
- Self-hosted option means zero recurring cost for auth, ever
- Pre-built login UI with session management, MFA, and social login
Watch out for
- Self-hosting requires running a Java backend service alongside your app
- Smaller community and fewer integrations compared to Auth0 or Clerk
- Documentation covers the basics but thins out for advanced customization
Alternatives
More in Authentication
Auth0
Enterprise-grade auth that handles every login method — from social login to SAML SSO
Clerk
Drop-in auth with pre-built UI components — sign-up, sign-in, and user management in minutes
Firebase Auth
Google's authentication service with generous free limits and tight integration across the Firebase ecosystem