public function signCertificateRequest(CertificateRequest $certificateRequest)
    {
        $csrObject = $this->createCsrWithSANsObject($certificateRequest);

        if (!$csrObject || !openssl_csr_export($csrObject, $csrExport)) {
            throw new CSRSigningException(sprintf('OpenSSL CSR signing failed with error: %s', openssl_error_string()));
        }

        return $csrExport;
    }