public void OnAuthorization(AuthorizationFilterContext context)
        {
            HttpContext httpContext = context.HttpContext;
            AuthenticationInternalResult authresult = AuthenticationHelper.Authenticate(context);

            if (authresult != null)
            {
                if (authresult.IsRredirect)
                {
                    context.Result = new RedirectResult(authresult.RedirectUrl, true);
                    return;
                }
                else if (authresult.KeepUnauthenticated)
                {
                    IAuthenticationResult unauthenticatedResult = AuthenticationResult.Unauthenticated();
                    AuthenticationHelper.SaveAuthenticationResult(httpContext, unauthenticatedResult);
                    return;
                }
                else
                {
                    IAuthenticationResult authenticationResult = AuthenticationResult.Authenticated(authresult.Authenticator.Type, authresult.User);
                    AuthenticationHelper.SaveAuthenticationResult(httpContext, authenticationResult);
                    return;
                }
            }

            switch (FailedAction)
            {
            case AuthenticationFailedAction.KeepUnauthenticated:
            {
                IAuthenticationResult unauthenticatedResult = AuthenticationResult.Unauthenticated();
                AuthenticationHelper.SaveAuthenticationResult(httpContext, unauthenticatedResult);
                return;
            }

            case AuthenticationFailedAction.RedirectCAS:
                context.Result = new HttpCASRedirectResult();
                return;

            case AuthenticationFailedAction.Return403:
                context.Result = new HttpAuthenticationForbiddenResult();
                return;

            case AuthenticationFailedAction.CustomHandler:
            {
                List <Type> customAuthenticators = null;
                AuthenticationFailedHandlerAttribute[] handlers = null;
                switch (context.ActionDescriptor)
                {
                case ControllerActionDescriptor controllerActionDescriptor:
                    customAuthenticators = GetCustomAuthenticators(controllerActionDescriptor);
                    handlers             = GetCustomHandlers(controllerActionDescriptor);
                    break;

                case CompiledPageActionDescriptor compiledPageActionDescriptor:
                    customAuthenticators = GetCustomAuthenticators(compiledPageActionDescriptor);
                    handlers             = GetCustomHandlers(compiledPageActionDescriptor);
                    break;

                default:
                    throw new Exception($"not handled with action descriptor of type {context.ActionDescriptor.GetType().Name}");
                }

                if (handlers != null && handlers.Length > 0)
                {
                    IActionResult actionResult = AuthenticationHelper.ExecuteHandler(handlers[0].Handler, handlers[0].ConstructParameters, httpContext, Policy, customAuthenticators.ToArray());
                    if (actionResult != null)
                    {
                        context.Result = actionResult;
                        return;
                    }
                    else
                    {
                        // not handled
                        throw new Exception($"not handled");
                    }
                }
            }
                return;
            }
        }