app\Certificate::getExpirationDate PHP Method

    public function getExpirationDate()
    {
        if (!is_file($this->getPath() . "/cert.pem")) {
            return null;
        }
        $data = openssl_x509_parse(file_get_contents($this->getPath() . "/cert.pem"));
        $dt = new \DateTime();
        $dt->setTimestamp($data["validTo_time_t"]);
        return $dt;
    }