private function cspGenerateNonce()
    {
        $nonce = base64_encode(
            openssl_random_pseudo_bytes(30, $isCryptoStrong)
        );

        if ( ! $isCryptoStrong)
        {
            $this->addError(
                'OpenSSL (openssl_random_pseudo_bytes) reported that it did
                <strong>not</strong> use a cryptographically strong algorithm
                to generate the nonce for CSP.',

                E_USER_WARNING
            );
        }

        return $nonce;
    }