code: func (refreshHandler *refreshCredentialsHandler) handlerFunc() func(message *ecsacs.IAMRoleCredentialsMessage) {
  	// return a function that just enqueues IAMRoleCredentials messages into the message buffer
  	return func(message *ecsacs.IAMRoleCredentialsMessage) {
  		refreshHandler.messageBuffer <- message
  	}
  }
docs: // handlerFunc returns the request handler function for the ecsacs.IAMRoleCredentialsMessage