ASP.NET WebAPI Basic-Authentifizierung schlägt immer fehl, da 401/Unauthorized

Versuchen, zum sichern meiner ASP.NET Web-API-2 Standardauthentifizierung verwenden, aber es endet immer mit Fehler:

401/Unauthorized
Authorization has been denied for this request.

Unten sind meine controller und ajax-request-code-snippet neben den request-und response-Header.

BasicAuthenticationHandler.SendAsync läuft immer sehr erfolgreich-bis:

return base.SendAsync(request, cancellationToken);

Q: WARUM Dann landet es als 401/unauthorized ?

Wenn ich entfernen [Autorisieren] aus der controller-action, dann funktioniert es aber ohne Sicherheit.

Hinweis: Da dies eine cross-domain-Anfrage, so habe ich aktiviert CORS auf der server-Seite.

Meine Authentication Handler

protected override System.Threading.Tasks.Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
{
    var principal = Thread.CurrentPrincipal;
    if (principal.Identity.IsAuthenticated)
    {
        return base.SendAsync(request, cancellationToken);
    }

    var encryptedTicket = ExtractToken(request.Headers.Authorization); //simply returns a string
    if (encryptedTicket != null)
    {
        var ticket = FormsAuthentication.Decrypt(encryptedTicket);
        var serializer = new JavaScriptSerializer();
        var user = serializer.Deserialize<UserInfoModel>(ticket.UserData);

        if (user != null)
        {
            var identity = new GenericIdentity(user.UserName, "Basic");
            Thread.CurrentPrincipal = new GenericPrincipal(identity, new string[0]);
        }
    }

    //Code reaches here always successfully but after this line errors Unauthorized
    return base.SendAsync(request, cancellationToken);
}

Mein Controller

public class ProductController : ApiController
{

Product[] products = new Product[] 
{ 
    new Product { Id = 1, Name = "Tomato Soup", Category = "Groceries", Price = 1 } 
};

[Authorize]
[Route("test/products")]
[EnableCors(origins: "*", headers: "*", methods: "*")]
public IEnumerable<Product> GetAllProducts()
{
    return products;
}
}

Mein AJAX-Request

$.ajax({
    type: "GET",
    url: "http://webapi.server.com/test/products",
    crossDomain: true,
    dataType: "json",
    contentType: "application/json; charset=utf-8",
    headers: { Authorization: "Basic 1234567890" },
    success: function (data) {
            alert(data);
    },
    error: function (err) {
            alert(err);
    }
});

Request-Header

Accept  application/json, text/javascript, */*; q=0.01
Accept-Encoding gzip, deflate
Accept-Language en-US,en;q=0.5
Authorization   Basic 1234567890
Content-Type    application/json; charset=utf-8
Host    webapi.server.com
Origin  local-pc
Referer local-pc/Index.aspx
User-Agent  Mozilla/5.0 (Windows NT 6.2; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0

Antwort-Header

Access-Control-Allow-Orig...    *
Cache-Control   no-cache
Content-Length  61
Content-Type    application/json; charset=utf-8
Date    Thu, 07 Nov 2013 11:48:11 GMT
Expires -1
Pragma  no-cache
Server  Microsoft-IIS/8.0
X-AspNet-Version    4.0.30319
X-Powered-By    ASP.NET