Pull the href attribute out of an html link element.
function _openid_link_href($rel, $html) {
$rel = preg_quote($rel);
preg_match('|<link\\s+rel=["\'](.*)' . $rel . '(.*)["\'](.*)/?>|iUs', $html, $matches);
if (isset($matches[3])) {
preg_match('|href=["\']([^"]+)["\']|iU', $matches[3], $href);
return trim($href[1]);
}
return FALSE;
}