Unauthorized access access denied redirect to URL ASP.NET C#

web.config

<customErrors mode="On" defaultRedirect="~/GenericErrorPage.htm" >

  <error statusCode="401" redirect="~/unauthorized.htm"/>

 </customErrors>

aspx.cs code

protected void Page_Load(object sender, EventArgs e)

{

if (!Page.IsPostBack)

{

if (Request.IsAuthenticated && !string.IsNullOrEmpty(Request.QueryString["ReturnUrl"]))

Response.Redirect("~/unauthorized.aspx");

}

}

or

public static bool CheckPageAccess(string uRL, long roleCode)

        {

            bool IsAllow = false;

            if (HttpContext.Current.Session[Constants.UserInformation] != null)

            {

                IsAllow = MenuService.MenuAccess(uRL, roleCode);

            }

            return IsAllow;

        }

if (!PageUtils.CheckPageAccess(Request.Url.AbsolutePath, CurrentUser.RoleMasterId))

                {

                    Response.Redirect("~/UnauthorizedAccessError.aspx?contentPage=" + Request.RawUrl);

                }

                if (!string.IsNullOrWhiteSpace(Request.QueryString["ApplicationId"]))

                {

                    ApplicationId = Convert.ToInt64(CryptologyFunctions.Decrypt(Request.QueryString["ApplicationId"]));

                }

 reference:- https://weblogs.asp.net/gurusarkar/redirect-unauthorized-users-to-access-denied-page-instead-of-login-page