How to implement session like stackoverflow?

I'm implementing this kink of login: http://jaspan.com/improved_persistent_login_cookie_best_practice

In this design a new token issued to the user each new login. So it tells me that I need to

Now I need to implement a session, for this login.

I'd like to implement session like stackoverflow, so people can have session as soon as they entered the site开发者_StackOverflow中文版, so they don't must to register.

Any ideas how?

I'm going to take a complete stab in the dark here and assume "have a session without a login" is referring to StackOverflow's use of OpenID, which enables you to share one set of login credentials across websites. The user still has a session, but it's the OpenID provider who does the authentication.