title: Firebase JS SDK OAuth2 request parameters: access_type: 'offline'
body: <p>I am building a serverless React PWA, where cloud functions manipulate API Resources (such as Classroom). And I am having a trouble gaining that offline authorized access. 
  Seems that <code>firebase-web</code> method <code>signInWithPopup</code> that takes in Authentication Provider <code>GoogleAuthProvider()</code> does not support application of custom fields to the request such as <code>access_type</code>, <code>state</code>, <code>scope</code>. </p>
  
  <pre><code>this.auth.googleAuthProvider.setCustomParameters({
              access_type: "offline"
          }) //doesn't work
  </code></pre>
  
  <p>Is it possible to modify AuthProvider's request such that I receive my <code>refresh_token</code> back?</p>