Can I offer the authentication, authorization, etc created using "ASP.NET MVC Open Id website" extension.. as a REST service in ASP.NET MVC? How can I create this service(maybe using WCF)? (Please if you can, offer me some examples please).
Yes, you can. OpenID is not about authorizing web services at all. That's what OAuth does. But DotNetOpenAuth does both OpenID and OAuth, so your users can authenticate with OpenID, then authorize RESTful clients via OAuth, and the user story is probably exactly what you're looking for.
There is a project template that shows you exactly how to do it (does it for you, actually) available on the Visual Studio Gallery.
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