public class MemberValidationAttribute : AuthorizeAttribute

     {

         protected override bool AuthorizeCore(HttpContextBase httpContext)

         {

             object user = HttpContext.Current.Session["CurrentUser"];

             if (user != null)

             {

                 return true;

             }

             return false;

         }

     }

 <system.web>

  <authentication mode="Forms">

       <forms loginUrl="~/Member/Login" timeout="2880" />

     </authentication>

 </system.web>