code: async def register(self):
          
          url = '{}/Sessions'.format(self.construct_url(API_URL))
          params = {'api_key': self._api_key}
  
          reg = await self.api_request(url, params)
          if reg is None:
              self._registered = False
              _LOGGER.error('Unable to register emby client.')
          else:
              self._registered = True
              _LOGGER.info('Emby client registered!, Id: %s', self.unique_id)
              self._sessions = reg
  
              # Build initial device list.
              self.update_device_list(self._sessions)
  
              asyncio.ensure_future(self.socket_connection(), loop=self._event_loop)
docs: Register library device id and get initial device list.