code: def _add_entity_id(self, config, co_name):
          
          base_entity_id = config['entityid']
          co_entity_id = "{}/{}".format(base_entity_id, quote_plus(co_name))
          config['entityid'] = co_entity_id
  
          return config
docs: Use the CO name to construct the entity ID for the virtual IdP
          for the CO.
  
          The entity ID has the form
  
          {base_entity_id}/{co_name}
  
          :type config: satosa.satosa_config.SATOSAConfig
          :type co_name: str
          :rtype: satosa.satosa_config.SATOSAConfig
  
          :param config: satosa proxy config
          :param co_name: CO name
  
          :return: config with updated entity ID