code: def sign_cert_request(filepath, cert_req, ca_crt, ca_key, days, extfile,
                        silent=False):
      
      message = 'sign certificate request'
      cmd = ('openssl x509 -req -in {} -CA {} -CAkey {} -CAcreateserial'
             ' -out {} -days {} -extfile {} -extensions v3_req').format(
                 cert_req, ca_crt, ca_key, filepath, days, extfile)
      call_openssl(cmd, message, silent)
docs: generate self signed ssl certificate, i.e. a private CA certificate
      :param filepath: file path to the key file
      :param keyfile: file path to the private key
      :param days: valid duration for the certificate
      :param silent: whether to suppress output