@mathieug I've been working on a similar part of our code today. It looks like you only get a refresh_token in the response on the first authorisation. 

Assuming you're using one of your own google accounts to test this, go to - https://myaccount.google.com/permissions and revoke the permissions your app has to your personal google account.

Then try to run the auth again from your project, you should see a refresh_token in the response if that was the issue!

EDIT: Here's a stack overflow question on the same topic - https://stackoverflow.com/questions/10827920/not-receiving-google-oauth-refresh-token#comment56214632_10857806

Originally posted by @katpas in #750 (comment)