hd works for OAuth2 FWIW:

https://github.com/dropbox/changes/commit/42c5dcddb86bb0830a6805d987ce517dab987e20

Ah, nice.

This is straightforward and probably <1 hour of work. It can be squeezed in if approved for prioritization.

The onscreen instructions for this adapter in the UI are also a bit out of date because the Google console has been updated since we wrote them. This is probably the next change to touch the provider, and should also look at modernizing the instructions.

Since T13227 has an actual realtime deadline, that's probably a good time to take care of this, too.

As of early 2020, this change works:

   public function getExtraAuthenticateParameters() {
     return array(
       'response_type' => 'code',
+      'hd' => 'epriestley.com',
     );
   }

So this is just an issue of adding a UI control.