old_contents: class Handler(object):
      """Handler class."""
  
      def __init__(self, transport, token, options):
          self._transport = transport
          self._token = token
          self.options = options
  
      def handle_connected(self):
          raise NotImplementedError
  
      def handle_event(self, event):
          raise NotImplementedError
  
new_contents: class Handler(object):
      """Handler class."""
  
      def __init__(self, transport, token, options):
          self._transport = transport
          self._token = token
          self.options = options
  
      def refresh_token(self):
          self._token.refresh()
          return self._token.access_token()
  
      def handle_connected(self):
          raise NotImplementedError
  
      def handle_event(self, event):
          raise NotImplementedError
  
subject: Add refresh_token method