<?php

$html = '<html>
<head></head>
<body>
<a href="https://w...content-available-to-author-only...e.com/user.asp?ref=fvFCF9D8N4Ak">bubu</a>
</body>
</html>';

$dom = new DOMDocument;
@$dom->loadHTML($html);

foreach ($dom->getElementsByTagName('a') as $tag) {

    $href = $tag->getAttribute('href');

    if (!empty($href)) {

    	echo $queryString = parse_url($href, PHP_URL_QUERY);
    }
}

