docs: def _verify_sector_identifier(self, request):
          """
          Verify `sector_identifier_uri` is reachable and that it contains 
          `redirect_uri`s.
  
          :param request: Provider registration request
          :return: si_redirects, sector_id
          :raises: InvalidSectorIdentifier
          """
          si_url = request["sector_identifier_uri"]
          try:
              res = self.endpoint_context.httpc.get(si_url)
          except Exception as err:
              logger.error(err)
              res = None
  
          if not res:
              raise InvalidSectorIdentifier("Couldn't read from sector_identifier_uri")
  
          logger.debug("sector_identifier_uri => %s", sanitize(res.text))
  
          try:
              si_redirects = json.loads(res.text)
          except ValueError:
              raise InvalidSectorIdentifier(
                  "Error deserializing sector_identifier_uri content")
  
          if "redirect_uris" in request:
              logger.debug("redirect_uris: %s", request["redirect_uris"])
              for uri in request["redirect_uris"]:
                  if uri not in si_redirects:
                      raise InvalidSectorIdentifier(
                          "redirect_uri missing from sector_identifiers")
  
          return si_redirects, si_url