protected void LoginOrders_Authenticate(object sender, AuthenticateEventArgs e)
        {
            bool result = false;
            result = Authentication(LoginOrders.UserName, LoginOrders.Password);

             if (result == true)
                 {
                      
                      e.Authenticated = true;
                      
                     Session["Check"] = true;
                }
               else
                    
                    e.Authenticated = false;
           }

            private bool Authentication(string login,string password)
            {
                //int r;
                string constring = "Data Source=хххх;Initial Catalog=хх;User ID=sa;Password=sa;Connect Timeout=10;TrustServerCertificate=True";
 	            string sqlstr;
                sqlstr = "Select [LOGIN], [PASSWORD] FROM [хх].[хх].[хх] WHERE [LOGIN]='" + login + "' AND [PASSWORD]='" + password + "'";
                SqlConnection con = new SqlConnection(constring);
                SqlCommand comm = new SqlCommand(sqlstr, con);
                SqlDataReader reader;

                try
                {
                    con.Open();
                    reader = comm.ExecuteReader();
                    if (reader.Read())
                        return true;
                    else
                        return false;
                }
                catch 
                { 
                    Exception ex;
                    return false;
                }

                finally
                {
                    con.Dispose();
                }
            }

   sqlstr = "Select [LOGIN], [PASSWORD] FROM [хх].[хх].[хх] WHERE [LOGIN]='" + login + "' AND [PASSWORD]='" + password + "'";

<authentication mode="Forms">
      <forms name=".ASPXFORMSDEMO" loginUrl="Login.aspx" protection="All" path="/" timeout="30"/>
    </authentication>
    <authorization>
      <deny users="?"/>
    </authorization>