Which Authentication Providers to Use for Single Sign In?

Question

I recently was tasked to implement Single Sign In functionality where users could register and sign in to this site using their credentials from a more popular site. That got me to start looking and asking around as to who was doing Single Sign In. I was surprised to learn how much of a hot button topic it turned out to be.

If you have rolled out Single Sign In for a web application, then which authentication providers did you end up using and why?

Answer 1

Try OpenID, stackoverflow uses it as well.

Answer 2

OpenID is very good if its an internet application. Lets users use things like their google account to log into yours.

If it is an intranet application then Windows Auth is fairly common but it works best with IE.