Supabase Auth vs Firebase Auth

Who Should Use Which

Use Supabase Auth if you're building a web app on Postgres and want auth that integrates directly with database-level security (Row Level Security). Best for apps where data access control is the core security model.

Use Firebase Auth if you're building a mobile app and need the most battle-tested mobile auth SDKs. Best for iOS/Android apps that need anonymous auth, phone verification, and deep mobile integration.

The Core Difference: RLS Integration

Supabase Auth's defining feature is its integration with Row Level Security. When a user authenticates, their identity flows directly into Postgres RLS policies. You write SQL like `WHERE auth.uid() = user_id` and the database enforces access control at the query level.

This means your application code doesn't need to check permissions - the database does it. Every query, whether from your API, a serverless function, or a direct Supabase client call, respects the same security boundary. This is genuinely more secure than application-level authorization.

Firebase Auth doesn't have an equivalent. Firestore Security Rules are separate from your data queries. You write rules in a custom language, test them separately, and they operate as a layer on top of your data access rather than being integrated into it.

For web applications with complex data access patterns - multi-tenant SaaS, collaborative tools, permission hierarchies - Supabase Auth + RLS is architecturally superior.

Auth Methods

Both support the standard methods: email/password, social login (Google, GitHub, Apple, etc.), phone/SMS auth, and magic links.

Firebase Auth adds anonymous auth - letting users interact with your app before creating an account, then upgrading to a full account later. This is particularly useful for mobile onboarding flows. Supabase doesn't have anonymous auth natively.

Supabase Auth supports SAML SSO on the Pro plan ($25/month). Firebase Auth supports multi-tenancy on the Blaze plan but SAML SSO requires Identity Platform, which is a separate (and more expensive) Google Cloud product.

Mobile SDKs

Firebase Auth's mobile SDKs are more mature. The iOS and Android libraries handle edge cases that matter in mobile: app state restoration after backgrounding, deep link handling for email verification, and smooth social login flows with native UI components.

Supabase Auth's mobile SDKs work but are younger. The Flutter and React Native clients are solid for basic auth flows. Complex mobile scenarios (biometric auth, app clips, Instant Apps) may require more custom work.

If you're building a native mobile app, Firebase Auth's SDK maturity is a genuine advantage.

Pricing

Supabase Auth is included with your Supabase project. Free plan: 50K MAUs. Pro plan ($25/month): 100K MAUs. That $25 includes your database, auth, storage, and realtime - not just auth.

Firebase Auth's Spark plan gives you 10K phone verifications per month for free (email and social are unlimited). Blaze (pay-as-you-go) charges $0.01-0.06 per phone verification beyond free limits.

For email-based auth, both are effectively free at reasonable scale. For phone/SMS auth at volume, Firebase's per-verification pricing can add up. Supabase includes phone auth in the base plan.

The Verdict

Supabase Auth wins for web applications where database-level security (RLS) matters. The auth-to-database integration is architecturally cleaner than any alternative. If you're building a SaaS with Postgres, Supabase Auth is the natural choice.

Firebase Auth wins for native mobile apps where SDK maturity, anonymous auth, and deep platform integration reduce development time. The iOS and Android SDKs are more battle-tested.

Most web developers should default to Supabase Auth. Most mobile developers should default to Firebase Auth.