我在LWP :: UserAgent中使用cookie时出了什么问题？

Question

在真正的Firefox浏览器中，我通过“ https://www.briefing.com/Login/subscriber.aspx”进行的身份验证在我的硬盘上放置了一个cookie。然后，当我开始另一个会话时，我可以绕过身份验证步骤，直接进入“ https://www.briefing.com/investor/calendars/earnings/2018/08/09”之类的数据页面。

在下面的代码中，我试图复制上面的内容，但无济于事。我在做什么错了？

use strict;
use warnings;
use HTTP::Cookies;
use LWP::UserAgent;

my $ua = LWP::UserAgent->new;

# Let ua use cookies and gives it an empty jar
$ua->cookie_jar(HTTP::Cookies->new());

# login to create cookies
# The field names are guessed, based on these web elements: 
# <input name="_textBoxUserName" id="_textBoxUserName" type="text">  
# <input name="_textBoxPassword" id="_textBoxPassword" type="password">   
my $url = 'https://www.briefing.com/Login/subscriber.aspx';
my $res = $ua->post($url,
                    '_textBoxUserName' => '*******',
                    '_textBoxPassword' => '*******');

# confirm that new cookies are indeed placed in the cookie jar
print join("\n", $ua->cookie_jar()->as_string);

# But URL still gets re-directed even though the cookie jar has been filled
$url = 'https://www.briefing.com/investor/calendars/earnings/2018/08/09';
$res = $ua->get($url);
print $res->content;