Add Google Calendar Javascript API OAuth Support to Free/Busy

Hello! I have a website that shows a bunch of hard-coded Google Calendar free/busy statuses, with the location of where the events are, and when the events end. It works well right now with public calendars. I would like to add OAuth to my Javascript so that the web page shows any the status of any calendars that are shared with me (not just public calendars). Most of the difficult code is already in place; I just need you to implement OAuth2 (I have an API key), and to modify the queries to allow for them to have authenticated requests instead of public ones. Feel free to ask with any questions you may have.