How it works
Firebase Authentication keeps users in your Firebase project and supports email and password, email link sign-in, phone numbers with SMS codes, anonymous accounts, and providers such as Google, Apple, Facebook, GitHub, Microsoft and X. Custom tokens let an existing login system hand its users over. FirebaseUI offers ready-made sign-in screens, and the SDKs keep people signed in and refresh their tokens automatically.
Each signed-in user has an ID token, a JWT valid for an hour, which Firestore and Cloud Storage security rules read as request.auth and which your own server can verify with the Admin SDK. Upgrading to Firebase Authentication with Identity Platform adds multi-factor authentication, SAML and OpenID Connect providers, blocking functions that run your code during sign-up and sign-in, audit logs, multi-tenancy and an SLA, and switches billing to monthly active users.
Phone sign-in needs the pay-as-you-go Blaze plan and is billed per SMS, so projects should limit which countries may receive codes to keep SMS fraud down. Passkeys are not a built-in sign-in method. Users can be exported with the Firebase CLI, but passwords are hashed with a modified scrypt, so moving elsewhere takes planning.
Firebase Authentication pros and cons
Pros
- Mature mobile SDKs that handle sign-in state for you
- Email, social and anonymous sign-in are free on the standard product
- Works directly with Firestore and Cloud Storage security rules
- Anonymous accounts can be upgraded later without losing data
Cons
- Tied to Firebase and Google Cloud, which makes leaving harder
- MFA and SAML need the Identity Platform upgrade, which changes billing
- Phone sign-in bills per SMS and attracts fraud without country limits
- No built-in passkey sign-in
When to use Firebase Authentication
Pick it when
- Mobile apps already built on Firebase and Firestore
- Phone-number sign-in with SDKs that handle the whole SMS flow
- Prototypes that need sign-in working in an afternoon
Skip it when
- Your data lives in a SQL database outside Firebase
- You need passkeys or enterprise SSO without add-ons or upgrades
Firebase Authentication pricing
Free tier
Email, social and anonymous sign-in are free. Phone sign-in needs the Blaze plan and bills per SMS (about $0.01 in the US). The Identity Platform upgrade gives 50,000 monthly active users free, then about $0.0025 to $0.0055 each.
Firebase Authentication pricing page (opens in a new tab)Approximate, checked September 2026.What the other tools cost
Firebase Authentication vs the alternatives
Related terms
More in Auth and identity
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