form身份验证通过后，只能用FormsAuthentication.RedirectFromLoginPage

FormsAuthenticationTicket Ticket = new FormsAuthenticationTicket (1,"coffee",DateTime.Now, DateTime.Now.AddMinutes(20), false,UserRoles,"/") ;

string HashTicket = FormsAuthentication.Encrypt (Ticket) ;

HttpCookie UserCookie = new HttpCookie(FormsAuthentication.FormsCookieName, HashTicket) ;
cookie.Domain = ".VeVB.COm";

Response.Cookies.Add(UserCookie)

Response.Redirect (Context.Request["ReturnUrl"]) ;