HttpContext.Current.User.Identity.IsAuthenticated=false;

HttpContext.Current.User.Identity.Name==""

解释：当用户登录时，服务器为确认客户端通过验证要通过cookie向客户端写验证（Authenticat）信息,在登录页面刚验证完成后服务器 还没有把cookie 回发到Client，所以会没有值，当服务器第二次Response的时候，就会从客户端读取Cookie，要想有此Cookie还要在 web.config文件中配置相应的参数

<system.web>
    <authentication mode="Forms">
      <forms domain="bokoAdmin" timeout="20" loginUrl="Login.aspx" path="/"></forms>
    </authentication>

   <authorization>
      <allow users="*"/>
    </authorization>

<system.web>

程序验证：

            if (Membership.ValidateUser(tbx_username.Text.TrimEnd(), tbx_password.Text.TrimEnd()))
            {
               
                FormsAuthentication.SetAuthCookie(tbx_username.Text.TrimEnd(), true,FormsAuthentication.FormsCookiePath);
                FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(
    1, tbx_username.Text, DateTime.Now, DateTime.Now.AddMinutes(20), false, tbx_username.Text);
                // generate new identity
                FormsIdentity identity = new FormsIdentity(ticket);
                HttpCookie cookie = new HttpCookie(FormsAuthentication.FormsCookieName, FormsAuthentication.Encrypt(ticket));
                // write to client.
                Response.Cookies.Add(cookie);
                }

其中加粗体为主要语句，有此一句就可以实现HttpContext.Current.User.Identity.IsAuthenticated=true;