Firebase merge user account by email after the fact

Question

I have been using Firebase authentication for a while and I have been using Facebook and Google logins. When I started it was not possible (or I didn't know) that you can limit on account per email and took care of it with Firebase database security rules and some code. In the database now I only have one account per email, but in the authentication accounts I have multiples per email. I would like to merge them or after the fact add the one account per email rule. Is that possible? If yes, how? And if not, is there any work around? It would be great to let people merge accounts. Thanks!

Answer 1

It is possible to merge accounts with the same email, even after some accounts have been created in Firebase Authentication.

First step is to disallow multiple-accounts-per-email by changing the setting in your Firebase project console. The change will only be applied to new users - all existing users will still sign into their existing accounts as before.

Since your app only uses Google/Facebook login, you can safely delete unwanted authentication accounts from the Firebase Console. Assuming in your database there is an entry (userid_1, email), and in you authentication project there are two accounts for the email (userid_1, email, Google) and (userid_2, email, Facebook). You can delete the (userid_2, email, Facebook) account using the Firebase Console or Firebase admin SDK. All subsequent logins with the same email, no matter via Google or Facebook, will always return the userid_1 account.