$DOM = new DOMDocument;
$DOM->loadHTML($html);
$inputs = $DOM->getElementsByTagName('input');

$hiddenInputs = array();
for ($i = 0; $i < $inputs->length; $i++){
    $item = $inputs->item($i);
    $type = $item->getAttribute('type');
    $name = $item->getAttribute('name');
    $value = $item->getAttribute('value');

    if($type == 'hidden'){
        $hiddenInputs[$name] = $value;
    }
}