google api - When authenticating with oAuth and youtube, always get error : invalid_grant on 2nd auth attempt, why?

Question

As of yesterday, my application is able to authenticate with google (youtube) via oAuth 2.0 the first time no problem but the 2nd time (re-authentication, same app + same user), when I exchange the requestToken for an accessToken I get an error:

error : invalid_grant

I'm using:

grant_type = authorization_code

like they suggest. What used to happen, before 2 days ago, was on re-authentication the web page would say 'you've already authenticated with this application before, would you like to grant it access again?'. What has changed or what could I be doing wrong?

Answer 1

I found a way to fix this (at least for us). When redirecting to the accounts.google.com/o/oauth2/auth url, we had to add both approval_prompt=force and access_type=offline. If one was missing, we got no refresh token.

This url documents all of the parameters, but says nothing about the refresh token: http://code.google.com/apis/accounts/docs/OAuth2WebServer.html