Using the clients from DotNetOpenAuth.AspNet in ASP.NET MVC

gistfile1.cs

        [HttpPost]
        public void OAuth(string provider, string returnUrl)
        {
            var client = OAuthHelper.GetOAuthClient(provider);
            client.RequestAuthentication(
                HttpContext,
                new Uri(Url.QualifyAction("OAuthCallback", "Auth", new { provider = provider, returnUrl = returnUrl }))
            );
        }

        [HttpGet]
        public ActionResult OAuthCallback(string provider, string returnUrl)
        {
            var client = OAuthHelper.GetOAuthClient(provider);
            var result = client.VerifyAuthentication(HttpContext);

            if (result.IsSuccessful)
            {
                // check if we have a user
                var user = membership.FindUserWithLogin(AuthenticationProviders.Twitter, result.ProviderUserId);

                if (user == null) // if not, register them
                {
                    // meh
                }

                // sign them in 

                return SignInAndRedirect(user, AuthenticationProviders.Twitter, returnUrl, createPersistentCookie: true);
            }

            return new EmptyResult();
        }