How to reuse OAuth2 connection to create Google_Client

Hi,

I use https://github.com/dektrium/yii2-user/ to manage RBAC access and authentication by Google.
I would like to display the number of new mails in the GMail mailbox.

So is it possible to convert Yii2 OAuth connection to Google_Client (need to retrieve access_token and refresh_token) ?

Thanks for your help.
Herve