title: What to use on GoogleSignInOptions, requestIdToken or requestServerAuthCode, to achieve Authorization code flow (aka OAuth2 Explicit)?
body: <p>I have implementing the Android Google authentication using google.android.gms.auth. </p>
  
  <p>In the setting for GoogleSignInOptions I used till now requestIdToken, with the understanding that this implements OAuth2 Authorization Code flow. This means that it should be using what is known in OAuth2 RFC as response_type=code, code-based that later is validated in the backed.</p>
  
  <p>But digging more into this, I just saw that there is another option requestServerAuthCode, and by looking at it is closer to what I thought I am doing. </p>
  
  <p>Which of these achieves OAuth2 Authorization Code Flow?</p>
  
  <p>Thanks! </p>