How to store credential or cookies for many sites

I wish to bui开发者_开发知识库ld a site more like Stack Overflow with a blog/page/apps for every member, and built with MVC 3. All features will be combined with different sites. How can I do this, or how Stack Overflow do it? Recently, if I remember correctly, I read that they did it with HTML 5...

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I believe that the StackExchange sites including StackOverflow all use the OpenID authentication.

You can read a little about it on a recent codingHorror post about the internet drivers licence, or check out the OpenID site directly. Its a simple concept, let the user use credentials that they already have.