generate certificate request
    :param filepath: file path to the certificate request
    :param keyfile: file path to the private key
    :param silent: whether to suppress output

def gen_cert_request(filepath, keyfile, config, silent=False):
    """
    generate certificate request
    :param filepath: file path to the certificate request
    :param keyfile: file path to the private key
    :param silent: whether to suppress output
    """
    message = 'generate ssl certificate request'
    cmd = (
        'openssl req -new -key {} -out {} -subj "{}"'
        ' -extensions v3_req -config {}').format(
            keyfile, filepath, SUBJECT, config)
    call_openssl(cmd, message, silent)