title: What is the first parameter for Firebase.Auth.GoogleAuthProvider.GetCredential?
body: <p>The new Firebase for Unity support has just been released into Beta and I am trying to implement Auth with it. I already have a Google sign-in that implements the oauth2 flow using an auth code from <code>GooglePlayGames.PlayGamesPlatform.Instance.GetServerAuthCode</code> and sending it to a server that exchanges it for an access token using the <code>https://www.googleapis.com/oauth2/v4/token</code> endpoint.</p>
  
  <p>I assume this access token is the second parameter of the <code>Firebase.Auth.GoogleAuthProvider.GetCredential</code> method, but what is the ID Token that the first parameter is asking for? Is that the token obtained from <code>GooglePlayGames.PlayGamesPlatform.Instance.GetIdToken</code> (same as <code>GoogleAuthUtil.GetToken</code>, if my reading of the docs/code is correct)?</p>
  
  <p>If this is the case, why are both required? I thought the access token was all that was needed to authenticate a user with google cloud services and that the ID Token was being phased out.</p>
  
  <p>Edit: After some testing, I found that passing the ID Token obtained from <code>GooglePlayGames.PlayGamesPlatform.Instance.GetIdToken</code> does allow Firebase to authenticate. Problem is, it asks for the user's email address every time. I'd like to avoid this if possible.</p>
  
  <p>What is the difference between <code>GetToken</code>, <code>GetAccessToken</code> and <code>GetIdToken</code>, aside from the fact that <code>GetIdToken</code> requires a callback?</p>