Auth token renew

[changhoi]

Hello, I tried to find the reason why the token invalid log occurs so random (for me).
I know that the code = Unauthenticated desc = etcdserver: invalid auth token log is just warning, and token is renewed by client retry_interceptor.go.

Then why the log is not occur when the request term is short.

	// with `--auth-token-ttl 10`	
	cli := pkg.Must(pkg.NewClient())
	for range time.Tick(time.Second * 2) {
		// When request every 2 seconds, the warn log is not occur.
		// But, over 5 seconds, the warn log is occur.
		v := pkg.Must(cli.Get(context.Background(), "/key", clientv3.WithPrefix()))
		fmt.Printf("%+v\n", v)
	}

Is there server logic for renew the token expiration time?