title: How to Link Multiple Auth Providers to an Firebase Account?
body: <p>I am unable to to sucessfully to do , I followed the following steps as instructed on Firebase Docs: </p>
  
  <ol>
  <li>Signed in use using existing auth provider(<strong>my case:facebook</strong>).</li>
  <li>Complete the sign-in flow for the new authentication provider up to, but not including, calling one of the <code>Auth.signInWith</code> methods.(<strong>my case: i want to link email &amp; password and Google OAUth</strong>).  So this is the step i'm unclear about, I created a new provider using <code>var provider = new firebase.auth.GoogleAuthProvider();</code>  and I did not do <code>Firebase.auth().signInWithPopup(provider)</code> . </li>
  <li>Then to get authcredential for google I run <code>var credential = firebase.auth.GoogleAuthProvider.credential(
  googleUser.getAuthResponse().id_token);</code> (<strong>I get an undefined googleUser error</strong>) this error seems appropriate since I have not signed in using Google Oauth but thats what the 2nd steps states(not to signin) </li>
  <li>And then this command to link with the current user who is on a Facebook Provider <code>auth.currentUser.link(credential)</code></li>
  </ol>
  
  <p>My understanding is that currentUser needs to be linked to my existing Provider(Facebook). It seems that credential variable for google is never computed. Anyone with a functional code example would really help.  </p>