public function save(string $filename)
    {
        if ('' === $filename) {
            throw new \UnexpectedValueException('The filename to store the certificate is empty');
        }
        $certificado = $this->extract();
        if ('' === $certificado) {
            throw new \RuntimeException('The certificado attribute is empty');
        }
        try {
            if (false === file_put_contents($filename, $certificado)) {
                throw new \RuntimeException('file_put_contents returns FALSE');
            }
        } catch (\Throwable $error) {
            throw new \RuntimeException("Unable to write the certificate contents into $filename", 0, $error);
        }
    }