Security: It’s Getting Worse

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace BadAuthentication
{
    public partial class Login : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void loginButton_Click(object sender, EventArgs e)
        {
            if (AuthenticateUser(userNameTextBox.Text, passwordTextBox.Text))
            {
                Response.Cookies.Add(new HttpCookie("username", userNameTextBox.Text));
                Response.Cookies.Add(new HttpCookie("password", passwordTextBox.Text));
                Response.Cookies.Add(new HttpCookie("loggedin", "true"));
                Response.Redirect("Default.aspx");
            }
        }


        private bool AuthenticateUser(string username, string password)
        {
            return true;
        }

    }
}