Firebase on React Native

@priemskiyyy/anchor-firebase-react-native observes the Auth instance of @react-native-firebase/auth your application uses. It answers the signed-in user as a session of your project's issuer, hears every change through onIdTokenChanged, mints the user's ID token for each token profile only when the native SDK minted it for the session's user, and ends the session with signOut(). It never initializes Firebase and never signs anyone in: that stays with anchor.native, which is your Auth. In a browser, or with the Firebase JS SDK on React Native, use @priemskiyyy/anchor-firebase instead.

Install

pnpm add @priemskiyyy/anchor @priemskiyyy/anchor-firebase-react-native @react-native-firebase/app @react-native-firebase/auth

React Native Firebase needs its native modules: a development build or a bare app, never Expo Go. The adapter supports @react-native-firebase/auth 26.

Create an Anchor

React Native Firebase 26 exports only its modular API, so pass the instance getAuth() returns:

import { Anchor } from "@priemskiyyy/anchor";
import { firebase, idToken } from "@priemskiyyy/anchor-firebase-react-native";
import {
  getAuth,
  signInWithEmailAndPassword,
} from "@react-native-firebase/auth";

export const anchor = new Anchor({
  adapter: firebase({ sdk: getAuth(), tokens: { api: idToken() } }),
});

await anchor.start();
await signInWithEmailAndPassword(anchor.native, email, password);

The sign-in reaches Anchor through onIdTokenChanged; nothing needs anchor.sync().

Options

Option	Type	Default	What it does
sdk	Auth	required	The instance getAuth() or getAuth(app) returned.
user	(user: User) => TUser	a snapshot of the profile fields	Maps the Firebase user to the plain data a session carries. Return plain data, never the User itself.
tokens	Record<string, FirebaseIdToken>	none	The token profiles, each idToken().

Capabilities

Capability	Firebase on React Native
Observation	Push, through onIdTokenChanged: sign-in, sign-out, account linking and token refresh, as the native SDK reports them.
Token profiles	idToken(): the user's Firebase ID token.
Forced refresh	Yes: user.getIdTokenResult(true).
End	Local: signOut(), for this Firebase app on this device. No remote step: the client cannot revoke refresh tokens.
Navigation after end	Never.
Runtimes	iOS and Android, through React Native Firebase's native modules. Browsers and the Firebase JS SDK: @priemskiyyy/anchor-firebase.

How a session is mapped

Session	From React Native Firebase
principal.authority	https://securetoken.google.com/<projectId>, the issuer of your ID tokens, from auth.app.options.projectId
principal.subject	user.uid
principal.tenant	user.tenantId, the Identity Platform tenant, or null
context	none
user	{ uid, email, emailVerified, displayName, photoURL, phoneNumber }, or your mapper's result
guest	user.isAnonymous
impersonated	false

This is the mapping of @priemskiyyy/anchor-firebase, so one user is the same principal in a browser and in your app. Linking an anonymous user to an account keeps its uid but ends its guest session: Anchor replaces the session and gives it a new key.

Tokens

session.getToken(profile) checks that auth.currentUser is still the session's user, then calls user.getIdTokenResult(forceRefresh) and answers its token. React Native Firebase asks the native SDK for the token of whichever user it holds when the call runs, not of the user the JavaScript User stood for, so the adapter answers the token only when the claims the native SDK decoded from it name the session's uid. A token minted for someone else rejects with SESSION_CHANGED, and so does a native SDK that already holds no user (auth/no-current-user). The token's kind is id-token and its scheme is Bearer. An expired credential (auth/user-token-expired) rejects with INTERACTION_REQUIRED; any other failure rejects with TOKEN_FAILED and the React Native Firebase error as its cause.

Ending the session

session.end() calls signOut() only while auth.currentUser is the session's user and the native SDK, whose signOut() signs out whichever user it holds, still holds that user too, read from the claims of its ID token (or, when that token cannot be read, as offline with an expired one, from the mirror alone). A native switch between that check and signOut() is the window that remains. It answers { local: "completed", remote: "not-applicable", navigation: null }: this Firebase app signs out on this device only. When React Native Firebase holds someone else, the adapter signs nobody out and answers not-applicable, as it does when the native SDK refuses with auth/no-current-user because it signed out before JavaScript heard of it. Any other refusal rejects with END_FAILED. To revoke a user's refresh tokens everywhere, use revokeRefreshTokens from the Admin SDK on your server. Signing out of Firebase does not sign out of the Google, Apple or Facebook SDK the user signed in with; that stays with them.

Behavior

• The factory is cold: creating the adapter touches nothing on Auth.
• The native SDK restores its user itself. The first read awaits authStateReady(), which settles once the native SDK reported its first auth state, so a user still being restored is initializing, never signed-out.
• An app whose options have no projectId cannot start: start() rejects with START_FAILED and an INVALID_CONFIGURATION cause.
• A user profile change made with updateProfile reaches the session on the next token change or anchor.sync().
• React Native's EventEmitter calls its listeners in one loop without a catch, so a user mapper that throws while React Native Firebase reports a change asks Anchor for a read instead of keeping the change from your own listeners; the failed read is a diagnostic.
• React Native Firebase calls a listener it just added once on a microtask, even one removed before that; after dispose(), Anchor ignores that call.
• dispose() removes the onIdTokenChanged listener.

What Anchor does not normalize

Sign-in methods and the native provider SDKs, phone auth and verifyPhoneNumber, account linking, multi-factor enrollment and challenges, email verification, custom claims, the iOS keychain access group (useUserAccessGroup), the emulator, and ID token results beyond the token stay with React Native Firebase. Read them through anchor.native.

The adapter runs against a fake modelled on @react-native-firebase/auth 26.4.0 and against that package's own JavaScript in Node, never on a device; see the verification matrix and React Native and Expo. The package README is the reference.