Enabling OpenAuth and allowing the user to login via Google, Yahoo, Facebook etc. is an common occurrence in websites. Is there an open-source library or project which can be consumed or referred to for implementing this functionality in ASP.NET MVC with SQL Server repository?
Nerd Dinner by Scott Hanselman, Phil Haack, Rob Conery et.al. is a good fit for your need.
It is a ASP.NET MVC project using DotNetOpenAuth for the log-on entities DotNetOpenAuth supports.