Migrating Auth state from Firebase JS SDK to React Native Firebase

[rustygloves]

Our react-native app was previously using the JS SDK with reactfire

We are in the process of migrating to React Native Firebase. For the best user experience I am trying to persist the auth state across releases.

We are using custom tokens for authentication.

My current implementation is flawed, I realise now as the token stored in EncryptedStorage is the one that is returned from auth.createCustomToken(uid) on the backend, which I believe expires after an hour. The saving to EncryptedStorage is a legacy feature of the app which led me to believe this token is actually of use, but I do not think it is

This a simplification of the current implementation:

const authPersistenceKey = `firebase:authUser:${Firebase.apiKey[STAGE]}:[DEFAULT]`;

const signInWithToken = async (token: string) => {
  await auth().signInWithCustomToken(token);
};

export const checkForToken = async () => {
  let token = null;
  if (auth().currentUser) return; // already signed in

  try {
    // This is the custom token
    token = await EncryptedStorage.getItem(TOKEN);
    if (token) {
      await signInWithToken(token);
      return;
    }
  } catch (error) {
    await EncryptedStorage.removeItem(TOKEN);

    const legacyAuth = await AsyncStorage.getItem(authPersistenceKey);

    if (legacyAuth) {
      token = JSON.parse(legacyAuth)?.stsTokenManager?.accessToken;
      if (token) {
          await signInWithToken(token);
          return;
      }
    }
  }
};

My question is essentially, will it be possible to re-autenticate with the stsTokenManager.accessToken or stsTokenManager.refreshToken or do I need to create a backend function to generate a new custom token using information in the legacy persistence to verify the user?

Am I missing something entirely and there a simpler way to do this?