code: def create_new_content_property(self, content_id, content_property, callback=None):
          
          assert isinstance(content_property, dict)
          assert {"key", "value"} <= set(content_property.keys())
          return self._service_post_request("rest/api/content/{id}/property".format(id=content_id),
                                            data=json.dumps(content_property),
                                            headers={"Content-Type": "application/json"}, callback=callback)
docs: Creates a new content property. Potentially a duplicate at the REST API level of
          create_new_property.
          :param content_id (string): A string containing the id of the property content container.
          :param new_property_data (dict): A dictionary describing the new property for the content. Must have the keys
                                           "key" and "value".
          :param callback: OPTIONAL: The callback to execute on the resulting data, before the method returns.
                           Default: None (no callback, raw data returned).
          :return: The JSON data returned from the content/{id}/property endpoint,
                   or the results of the callback. Will raise requests.HTTPError on bad input, potentially.
  
          Example property data:
          {
              "key": "example-property-key",
              "value": {
                  "anything": "goes"
              }
          }