Authenticate User using Windows login credentials

 public static bool ValidateW(string UserName, string Password, string DomainName)
        {
            bool valid = false;
            try
            {
               
                if (UserName.IndexOf("\\") != -1)
                {
                    string[] arrT = UserName.Split(SPLIT_1[0]);
                    UserName = arrT[1];
                }
                using (PrincipalContext context = new PrincipalContext(ContextType.Domain, DomainName))
                {
                    valid = context.ValidateCredentials(DomainName+"\\" + UserName, Password);
                   
                }
               
            }
            catch (Exception ex)
            {
                throw ex;               
            }
            return valid;
        }

        bool GetEmployee()
        {
            bool flag = false;
            Entities.Employee data = null;
            string userName = UserName.Text;
            try
            {
                if (userName.IndexOf("@") != -1)
                {
                    string[] arrT = userName.Split(SPLIT_2[0]);
                    userName = arrT[0];
                }
                BusinessLayer.Employee emp = new BusinessLayer.Employee();
                data = emp.GetEmployee(userName);               
                flag = true;
            }
            catch (Exception ex)
            {
               
            }
            return flag;
        }
        protected void Button1_Click(object sender, EventArgs e)
        {
            try
            {
                if (ValidateW(UserName.Text, Password.Text, Domain.SelectedValue))
                {
                    if (GetEmployee())
                    {
                        if (Request.QueryString["ReturnUrl"] != null)
                        {
                            FormsAuthentication.RedirectFromLoginPage(UserName.Text, false);
                        }
                        else
                        {
                            FormsAuthentication.SetAuthCookie(UserName.Text, false);
                        }
                    }
                    else
                    {
                        FailureText.Text = "Your details does not exist in the system. Please contact Administrator.";
                    }
                }
                else
                {
                    FailureText.Text = "Your login attempt was not successful. Please try again.";
                }
            }
            catch (Exception ex)
            {
                throw;
            }
        }