code: def get_system_cert_file():
      
      if os.name == 'posix':
          filename = "/etc/ssl/certs/ca-certificates.crt"
          if os.path.isfile(filename):
              return filename
      msg = "no system certificate file found"
      raise ValueError(msg)
docs: Try to find a system-wide SSL certificate file.
      @return: the filename to the cert file
      @raises: ValueError when no system cert file could be found