DotnetOpenAuth is a open source library that allows the developers to add the OpenId and OAuth capabilities to their ASP.NET Web Application.
It allows the developers to include the OpenId support by just dragging and dropping a ASP.NET control to the Web Page.
The DotnetOpenAuth has a classic ASP support and also support for custom extensions.
Know more about DotnetOpenAuth – OpenId API for ASP.NET MVC Application here