XMLSecurityDSig::appendSignature PHP Method

    public function appendSignature($parentNode, $insertBefore = false)
    {
        $beforeNode = $insertBefore ? $parentNode->firstChild : null;
        return $this->insertSignature($parentNode, $beforeNode);
    }

function signXML($token, $privkey)
{
    $sigdoc = new DOMDocument();
    if (!$sigdoc->loadXML($token)) {
        throw new Exception("Invalid XML!");
    }
    $sigNode = $sigdoc->firstChild;
    $enc = new XMLSecurityDSig();
    $enc->idKeys[] = 'ID';
    $enc->setCanonicalMethod(XMLSecurityDSig::EXC_C14N);
    $enc->addReference($sigNode, XMLSecurityDSig::SHA1, array('http://www.w3.org/2000/09/xmldsig#enveloped-signature', XMLSecurityDSig::EXC_C14N));
    $key = new XMLSecurityKey(XMLSecurityKey::RSA_SHA1, array('type' => 'private', 'library' => 'openssl'));
    $key->loadKey($privkey, false, false);
    $enc->sign($key);
    $enc->appendSignature($sigNode);
    return $sigdoc->saveXML();
}