HttpContext.Current.Response.Cookies.Add(new HttpCookie(FormsAuthentication.FormsCookieName, FormsAuthentication.Encrypt(authTicket)));

FormsAuthentication.SignOut();

userPrincipal.Identity.IsAuthenticated

Debug.Assert(HttpContext.Current.Request.IsSecureConnection, "oops, the IsAuthenticated is not working here");

if (HttpContext.Current.User.Identity.IsAuthenticated)
{

}