What is Firebase Authentication?

Firebase Authentication is a managed identity service that handles user sign-up, sign-in, and identity management. It supports multiple authentication providers: Email/Password, Google, Facebook, Twitter, GitHub, Apple, Microsoft, Phone (SMS OTP), Anonymous, and Custom Tokens (SAML/OIDC for enterprise SSO). Key features: (1) Firebase Auth handles session management — issues JWTs automatically; (2) Integration with Firestore security rules — request.auth.uid enables user-specific data access; (3) Multi-factor authentication (MFA) — supports TOTP and SMS-based MFA; (4) Email verification and password reset — built-in flows; (5) Auth state persistence — user sessions persist across app restarts. Firebase Auth eliminates the need to build and maintain a custom authentication system, reducing development time significantly.