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 us

Answer 1

I think I may have found the answer here:

https://groups.google.com/forum/#!searchin/oauth2-dev/invalid_grant/oauth2-dev/eaOa6THER0k/z4eO-taUFxgJ

The problem was that that the "code" parameter that you need to send needs to be encoded. It will work when you set the approval_prompt to force because the return code contains URL-safe characters. However, this is not the case for the return code upon a second authorization request.

For me this fixed it, I hope it does for you as well.

Answer 2

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