You should have some Redirect URL defined for Google to redirect to after the authentication is done. If you cant host your pages on any web site, you can very well host it in local host.
Regarding getting the access token from the popup to the main parent window, you can setup a timer in parent window which keeps on checking the document location of the popup. Once the document location matches the Redirect URL, u can parse the access token which will will be in the URL itself.
I wrote a tutorial on exactly the same problem (using local host) yesterday and here is the link:
http://www.gethugames.in/2012/04/authentication-and-authorization-for-google-apis-in-javascript-popup-window-tutorial.html
Hope you will find it useful.