no subject

Thank you for answering my question at http://dw-dev-training.dreamwidth.org/65408.html . I have questions about http://www.dreamwidth.org/export_comments?get=comment_body&startid=0 . Is there any way to get poster's name from posterid that is returned by export_comments? How do I determine which post the following comment belongs to?

<livejournal>
    <comments>
        <comment id="1" jitemid="0" posterid="123456" postid???>
            <body>Some Text.</body>
            <date>2004-05-21T22:29:57Z</date>
        </comment>
        ...
    </comments>
</livejournal>

If there's no way to get poster's name and post id for a given comment, is there a way to programmatically download a post page with all comments on it as if I'm logged in to DW? Suppose this is a private post: https://ari-linn.dreamwidth.org/535040.html?format=light&expand_all=1 If I were to download it, how do I authenticate?

GET https://ari-linn.dreamwidth.org/535040.html?format=light&expand_all=1 HTTP/1.1
Host: ari-linn.dreamwidth.org
Authorization: Basic base64_encode("user:password") ??? or do I somehow get a cookie from DW?