使用Cookie完成自动登录

//------------------------------登录页面----------------------------
        string username = this.txtUserName.Text;//用户名
        string password = this.txtPassword.Text;//密码

        if (UserManager.LoginValidate(username, password) && this.ckState.Checked == true)//判断登录名和密码是否正确和是否选择了记住用户名和密码的复选框
        {
           //判断客户端浏览器是否存在该Cookie 存在就先清除

            if (Request.Cookies["username"] != null && Request.Cookies["password"] != null)
            {
                Response.Cookies["username"].Expires = System.DateTime.Now.AddSeconds(-1);//Expires过期时间
                Response.Cookies["password"].Expires = System.DateTime.Now.AddSeconds(-1);
            }
            else
            {
                 //向客户端浏览器加入Cookie （用户名和密码 最好是使用MD5加密）
                HttpCookie hcUserName1 = new HttpCookie("username");
                hcUserName1.Expires = System.DateTime.Now.AddDays(7);
                hcUserName1.Value = username;
                HttpCookie hcPassword1 = new HttpCookie("password");
                hcPassword1.Expires = System.DateTime.Now.AddDays(7);
                hcPassword1.Value = password;
                Response.Cookies.Add(hcUserName1);
                Response.Cookies.Add(hcPassword1);
            }
}
                  

//------------------------转到登录后的页面（有母板页写母板页最好）------------------------
              if (Request.Cookies["username"] != null && Request.Cookies["password"] != null)
                {
                    //用户曾登录 
                 
                    username = Request.Cookies["username"].Value.ToString();  //读取Cookie 
                    password = Request.Cookies["password"].Value.ToString();//判断Cookie读取出来的用户名和密码是否能正确登录
                    if (UserManager.LoginValidate(username, password))
                    {
                      //登录后的代码
             }         }      

//-------------------------------Cookie退出（加一个退出按钮）-------------------------------      

        //退出
        HttpCookie hcUserName1 = new HttpCookie("username");
        hcUserName1.Expires = System.DateTime.Now.AddDays(-7);
        hcUserName1.Value = username;
        HttpCookie hcPassword1 = new HttpCookie("password");
        hcPassword1.Expires = System.DateTime.Now.AddDays(-7);
        hcPassword1.Value = password;
        Response.Cookies.Add(hcUserName1);
        Response.Cookies.Add(hcPassword1);