I wrote a little PowerShell script to retrieve an Access Token via OAuth 2.0 that may come in handy for someone else.  This script is specifically for the Google Groups Provisioning API, but can be adapted to other Google API’s, or any other API, by modifying the necessary variables to send a request in the required format. Get the script here:  https://dl.dropboxusercontent.com/u/5443945/powershell/getAccessTokenGoogleAPI.ps1