WebClient表单WebAPI中的身份验证

Web服务代码

[Authorize]
public class RegistrationController : ApiController
{
    [AllowAnonymous]
    [HttpPost]
    public string Get(string user,string pass)
    {
        if (user=="abc"&&pass=="cba")
            FormsAuthentication.SetAuthCookie("HomeUser", false);
        return "Home";
    }
    [HttpGet]
    public string Post()
    {
        return "Post";
    }
}

从控制台进行表单验证

class CookieWebClient : WebClient
    {
        public CookieContainer CookieContainer { get; private set; }
        /// <summary>
        /// This will instanciate an internal CookieContainer.
        /// </summary>
        public CookieWebClient()
        {
            this.CookieContainer = new CookieContainer();
        }
        /// <summary>
        /// Use this if you want to control the CookieContainer outside this class.
        /// </summary>
        public CookieWebClient(CookieContainer cookieContainer)
        {
            this.CookieContainer = cookieContainer;
        }
        protected override WebRequest GetWebRequest(Uri address)
        {
            var request = base.GetWebRequest(address) as HttpWebRequest;
            if (request == null) return base.GetWebRequest(address);
            request.CookieContainer = CookieContainer;
            return request;
        }
    }

该程序的目标是登录到Web服务，然后查询安全授权方法，然后重置授权。如何用最简单的方法做到这一点？

using (var client = new CookieWebClient())
        {
            var values = new NameValueCollection
{
    { "user", "abc" },
    { "pass", "cba" },
};
            client.UploadValues("http://localhost:1401/Get/","POST", values);
            // If the previous call succeeded we now have a valid authentication cookie
            // so we could download the protected page
            string result = client.DownloadString("http://localhost:1401");
        }

UploadValues行上有一个错误405未知方法。你能帮我吗？我通过表格的方式使用授权，因为我发现这种方法尽可能简单，同时又安全。

p.S.WebApiConfig代码：

config.MapHttpAttributeRoutes();
        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "{api}/{id}",
            defaults: new { controller="Registration",
                api=RouteParameter.Optional,
                id = RouteParameter.Optional }
        );
        config.Filters.Add(new AuthorizeAttribute());

config.Routes.MapHttpRoute(
    name: "DefaultApi",
    routeTemplate: "api/{controller}/{id}",
    defaults: new { id = RouteParameter.Optional }
);

client.UploadValues("http://localhost:1401/api/Registration/","POST", values);