Calling Google OAuth2 from javascript (No Access-Control-Allow-Origin)

Question

I'm attempting to use a public dataset in Google BigQuery and in order to do so I have to use OAuth2. However, I'm writing it entirely client-side, and would like to keep it that way if possible. Every time I try a request from the javascript, however, I get the usual "No Access-Control-Allow_Origin header present." Is it at all possible to get around this - or tell the API that I want such a header? I thought that that was what "Javascript origins" in the developer console did, but I guess not. Can I get this to work, or am I screwed and have to use a backend or installed application?