Single sign on Google

How does the Google single sign on works (OR any website's SSO)? For example, once I login to the Gmail, it lets me see "My places" on Google Maps without signing in again? Same with Yahoo mail and Yahoo notepad.

I am guessing this checki开发者_如何学Cng is done locally within the browser. But any more details would be appreciated.

It is done with a cookie, that is accessible to all sub-sites on google, and it contains identification numbers. Then the sub-site queries the account server, gives the cookie, and the account server will return the user.

Actual implementation details may vary (as I am not a Google engineer), but I think you want to know how to do it, not what google does.