Custom Authentication Attributes in ASP.NET MVC

RequiresAuthenticationAttribute.cs

namespace YourProject.Models
    {
        public class RequiresAuthenticationAttribute: ActionFilterAttribute
        {
            public override void OnActionExecuting(ActionExecutingContext filterContext)
            {
                string LoginPath = "/Login";    //  Path to your login page

                //  Check authentication
                Authentication auth = new Authentication(); 
                //  ^ Your Custom authentication class
                if (!auth.isAuthenticated()) /* <<< Your authentication condition */
                {
                    //  Not authenticated
                    //  Need to login, redirect away from the 
                    //  controller action!
                    Debug.Print("Authentication REQUIRED!");
                    filterContext.Result = new RedirectResult(LoginPath);
                }
                else
                {
                    //  Authenticated
                    // If we get here, the attribute will end, and 
                    // defer execution back to the controller action
                    // from which it was invoked.
                    Debug.Print("User is authenticated");
                }
            }
        }
    }