code: func (s *SeesawECU) ConfigSource(args *ipc.ConfigSource, oldSource *string) error {
  	if args == nil {
  		return errors.New("args is nil")
  	}
  	ctx := args.Ctx
  	s.trace("ConfigSource", ctx)
  
  	authConn, err := s.ecu.authConnect(ctx)
  	if err != nil {
  		return err
  	}
  	defer authConn.Close()
  
  	source, err := authConn.ConfigSource(args.Source)
  	if err != nil {
  		return err
  	}
  
  	if oldSource != nil {
  		*oldSource = source
  	}
  	return nil
  }
docs: // ConfigSource requests the configuration source be changed to the specified
  // source. The name of the original source is returned.