code: def _access_token(self, request: Request=None, page_id: Text=''):
          
  
          if not page_id:
              msg = request.message  # type: FacebookMessage
              page_id = msg.get_page_id()
  
          page = self.settings()
  
          if page['page_id'] == page_id:
              return page['page_token']
  
          raise PlatformOperationError('Trying to get access token of the '
                                       'page "{}", which is not configured.'
                                       .format(page_id))
docs: Guess the access token for that specific request.