gapi.auth2 can not get access_token

I'm trying to implement resumable uploads for youtube using the javascript client API. I've managed to get the login working using the g-signin2 button, but I can't get the access_token to send with the requests. This is how I render the sign in button:

<span
  class="g-signin2"
  data-onsuccess="youtubeUploaderSigninCallback"
  data-scope="https://www.googleapis.com/auth/youtube.upload https://www.googleapis.com/auth/youtube">
</span>

And I'm using the following script files loaded from google (I can't seem to get one working without the other)

<script src="https://apis.google.com/js/platform.js" async defer></script>
<script src="https://apis.google.com/js/client.js" async defer></script>

I'm using code edited samples from https://developers.google.com/youtube/v3/code_samples/javascript#upload_video for resumable uploads using XHR. But these examples use the auth functions marked as deprecated here: https://developers.google.com/api-client-library/javascript/reference/referencedocs So the main thing I changed is using the auth2 and g-signin2 instead of result.access_token and g-signin.

So I've been trying to use the auth2 functions to get the access tokens, but the access_token property is undefined when I execute the following code

gapi.auth2.getAuthInstance().currentUser.get().getAuthResponse()

The way I'm trying to get the access token is documented here: https://developers.google.com/api-client-library/javascript/features/cors#making-authenticated-requests

So these are my options, I guess:

1. find a way to get the access token out of the user object
   • (I found that user.hg.access_token contains the token I need
   • but "hg" seems a minified property to me
   • so I'm not intending to use this as it might change with updates
   • EDIT: as pointed out in the comments hg is a minified property indeed and now no longer exists
2. add progress events to gapi.client.request()
   • but the xhr object doesn't seem to be exposed
3. use code documented as deprecated

Can anyone help me with this? I've been looking for an acceptable solution for a few hours and I feel like crying now... all alone and desperate.

Thanks in advance, Robbe

PS: I've also posted this question on google groups