Perl - how do I close a connection to Jazz?

I'm using Perl 5.22 and CLM 4.0.7 running under WAS 8.8.5.9.

I have a long-running Perl program interrogating RM project areas via OSLC.  My problem is that after 8 hours an attempt to retrieve an XML doc via a GET to a URL returns an HTML structure instead, which looks rather like a logon prompt as it includes this: 

    <script type="text/javascript">
    / <![CDATA[ /
        dojo.addOnLoad( function() {
            net.jazz.ajax.ui.PlatformUI.createAndRunWorkbench("net.jazz.web.app.authrequired");
        });
    / ]]> /
    </script>

Interestingly, the structure is not valid XML but that's not really the issue.

I've tried to periodically refresh the login session by this method:
$userAgent->conn_cache(LWP::ConnCache->new());
but the job still fails after 8 hours so clearly that doesn't work.  Simply periodically reissuing the intial logon ($$response = $$userAgent->request(POST $jazzConnUri,[j_username=>$jazzuser, j_password=>$jazzpwd]);) doesn't work either, and in fact fails.

I think the answer is to periodically close then reopen the connection, but I can't work out what I need to post to make the close happen.  Can anyone help?  Or offer a better strategy?