Windows credentials

Question

Hi I have problem. In mz asmx web service I have method which return call user windows identity.

    [WebMethod]
    public string TestAuthenticated()
    {
    return User.Identity.Name;
    }

I test web service and client on the same pc on localhost. If I call web method TestAuthenticated from web broeser it return good user identity.

But if I call this method from winforms client it return empty string. I add user creadentials to the proxy object and then I call method :

        proxyObj.Credentials = CredentialCache.DefaultCredentials;
        Text = proxyObj.TestAuthenticated();

But the method TestAuthenticated return empty string, where can be problem. Any advice ? Thank