docs: def get_api_references(self, api_url=None):
          """Get set of HATEOAS reference for the given SCO-API. Use the default
          SCO-API if none is given. References are cached as they are not expected
          to change.
  
          Parameters
          ----------
  
          Returns
          -------
          """
          # Get subject listing Url for SCO-API
          if not api_url is None:
              url = api_url
          else:
              url = self.api_url
          # Check if API references are in local cache. If not send GET request
          # and add the result to the local cache
          if not url in self.apis:
              self.apis[url] = sco.references_to_dict(
                  sco.JsonResource(url).json[sco.REF_LINKS]
              )
          return self.apis[url]