I am creating a RESTful web interface for my ASP.NET MVC4 web application using ASP.NET WebAPI. I want to use OAuth 1.0 to provide authorization. I am looking at the DotNetOpenAuth library. Can someone help me understand how to use the service provider of this library with ASP.NET WebAPI?
I am in the same situation as you. I would recommend you take a look at the Thinktecture IdentityModel Power of Attorney Extensions for the Web API (and MVC).This is an open source project hosted on GitHub, with samples to take a look at.
You can also get a lot of useful information from the Dominick Baier blog.
Have you looked at the OAuthServiceProvider sample that ships with DotNetOpenAuth? It demonstrates the WCF service, which is protected by OAuth 1.0.