docs: def backup_download(self, filename=None):
          """Download backup file from WebDAV (cloud only)."""
          if self.deploymentType != 'Cloud':
              logging.warning(
                  'This functionality is not available in Server version')
              return None
          remote_file = self.backup_progress()['fileName']
          local_file = filename or remote_file
          url = self._options['server'] + '/webdav/backupmanager/' + remote_file
          try:
              logging.debug('Writing file to %s' % local_file)
              with open(local_file, 'wb') as file:
                  try:
                      resp = self._session.get(url, headers=self._options['headers'], stream=True)
                  except Exception:
                      raise JIRAError()
                  if not resp.ok:
                      logging.error("Something went wrong with download: %s" % resp.text)
                      raise JIRAError(resp.text)
                  for block in resp.iter_content(1024):
                      file.write(block)
          except JIRAError as je:
              logging.error('Unable to access remote backup file: %s' % je)
          except IOError as ioe:
              logging.error(ioe)
          return None