Here's the link: https://security.google.com/settings/security/permissions
This link allows you to revoke access to "apps" that you have granted access to your account. Similar to apps on Facebook, people using Google Accounts have to grant access to the app in order for your implementation to have access to data, or make changes.
Though I am sure that this link is provided somewhere in the documentation...I found it in a Stack Overflow question and it was extremely helpful when I wanted to test that my implementation was still working.
At some point I will try to write an in depth article on the other pain points of Google's APIs and documentation that doesn't provide the answers I need.