I recently started exploring OpenID/OAuth authentication/authorization concepts hoping to develop ASP.NET Web Form applications enabled for Single Sign One with OpenID Providers. A provider could be Google, Yahoo, Facebook, Myspace etc ... In this article, I will show you how to enable an ASP.NET Web Form's application to authenticate/authorize with OpenID Providers like Google, Yahoo, OpenID, myOpenID, Wordpress, etc ... I won't go into explaining OpenID standards as there are so many articles out in the jungle that you can grab & read. Therefore, what I will do is offer you some useful material that I will recommend you go over them to get the details of OpenID and its extensions.