docs: def create_csr(key_file, organization_name, common_name, serial_number, file_):
      """Create a CSR for a key, and save it into ``file``."""
      key = crypto.load_privatekey(crypto.FILETYPE_PEM, key_file.read())
  
      req = crypto.X509Req()
      subj = req.get_subject()
  
      subj.O = organization_name  # noqa: E741 (we can't do anything about this)
      subj.CN = common_name
      subj.serialNumber = serial_number
  
      req.set_pubkey(key)
      req.sign(key, 'md5')
  
      file_.write(crypto.dump_certificate_request(crypto.FILETYPE_PEM, req))