How would Google Multiple Accounts Sign-in be implemented?

Google published that they are testing a feature that allows you to sign in 开发者_JAVA百科simultaneously to multiple Google accounts in the same browser.

Any idea how would that be implemented ?

I don’t have any inside info on how multiple accounts are actually supported, but here’s what I presume:

1. Your cookie holds a security token, just like in the old days.
2. The security token now maps to a set of signed-in accounts on the server.
3. I’d guess there’s a notion of an active account among this set.
4. When you go to a Google service that implements multiple-account support, the service pulls down your active account and drops you into that account by default.
5. Then, you get presented with some UI that lets you toggle between your other signed-in accounts or lets you sign into a new account.