public static string ClientInformation(HttpListenerContext context)
{
    System.Security.Principal.IPrincipal user = context.User;
    System.Security.Principal.IIdentity id = user.Identity;
    if (id == null)
    {
        return "Client authentication is not enabled for this Web server.";
    }
    
    string display;
    if (id.IsAuthenticated)
    {
        display = String.Format("{0} was authenticated using {1}", id.Name, 
            id.AuthenticationType);
    }
    else
    {
       display = String.Format("{0} was not authenticated", id.Name);
    }
    return display;
}