title: Firebase - use two authentication providers for same user
body: <p>For a Firebase project containing two different applications, i need to activate two different authentication providers on the Firebase users.
  Currently i am able to set (via console) Google login provider <strong>OR</strong> mail/password provider, but never both on the same user.</p>
  
  <p>Funny part is one of the users (a developer with console access) has been able to enable it, so there must be a way, but we can't figure out how he did it. See the user with both providers in the screenshot below.</p>
  
  <p><a href="https://i.stack.imgur.com/nB8zB.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nB8zB.png" alt="current users on firebase"></a></p>
  
  <p>current auth methods:</p>
  
  <p><a href="https://i.stack.imgur.com/LzdWk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LzdWk.png" alt="auth methods"></a></p>
  
  <p>EDIT 14/10/2018</p>
  
  <p>The "one account per email address" setting was disabled. No luck.
  We tried this: <a href="https://firebase.google.com/docs/auth/android/account-linking" rel="nofollow noreferrer">https://firebase.google.com/docs/auth/android/account-linking</a></p>
  
  <p>but it seems we cannot make it work with node js.</p>
  
  <p>The third option suggested in the comments (use different projects for different apps) cannot be followed, as these are actually two related apps with some common components.</p>
  
  <p>after some troubleshooting i'm afraid i will just add some more weird stuff:
  1) With the option "one account per email address" disabled, i tried to delete my account then add it again with email\password, this succeded. Then i tried to login with google in the app: the login failed but in firebase i was able to see a new "empty" (no email) user, with a new UID.
  THEN i deleted all the accounts and tried to login with google in the app (normally it creates the account in firebase), result: login failed, empty account created. Deleted it, tried to create it manually on the console, result: "account already existing".</p>
  
  <p>So after this we just gave up and went for a different way to handle the authentication. Hope to find this working in the future, as it could be really useful for us.</p>