code: def _default_headers(self, content_type=CONTENT_TYPE, token=None):
          
          headers = {
              self.HEADER_CLIENT_TYPE: self.CLIENT_TYPE,
              self.HEADER_TIMESTAMP: str(self._now()),
              self.HEADER_CUSTOMER_APP_ID: token or self._token
          }
  
          if content_type is not None or content_type is not False:
              headers[self.HEADER_CONTENT_TYPE] = content_type
  
          return headers
docs: Get default headers for API request
          :param unicode content_type: HTTP request content type
          :param: str token: customer app ID
          :return: dictionary