Detect if user has passport

[Guest]

Hello,
I'm trying to use a very simple case of MS Passport:

Detect if a user is logged in via MS passport; if yes then return the
username, else redirect to the Microsoft-hosted login site.

This could theoretically be accomplished with a trivial API call, something
like:

string strUserName = GetLoggedInPassport();
if (strUserName == null){
//assume no logged in passport, redirect:
Response.Redirect(PassportManager.LoginPage);
} else {
//got a logged in username, proceed...
}

I see references to a Passport SDK, but they're all broken links. I also see
references to license fees, MS needing to certify your site, and a lot of
heavy things that make sense if it were a big enterprise app like Monster.com.

Does anyone know how I can implement these 5 lines of code?
Thanks,
Tim