etcd: clientv3 doesn't renew the auth token

The etcd clientv3 doesn’t renew the auth token when it expires, it just fails with invalid auth token. It happens with both simple and jwt token types.

Steps to reproduce:

1. Start etcd with etcd --auth-token simple --auth-token-ttl 5
2. Enable authentication

etcdctl user add root
etcdctl user  grant-role  root root
etcdctl auth enable
# Verify that it works
etcdctl --user root:root put test test
etcdctl --user root:root get test

1. Run the following Go program

package main

import (
	"context"
	"fmt"
	"log"
	"time"

	clientv3 "go.etcd.io/etcd/client/v3"
	"google.golang.org/grpc"
)

func main() {
	client, err := clientv3.New(clientv3.Config{
		Context:   context.Background(),
		Endpoints: []string{"127.0.0.1:2379"},
		Username:  "root",
		Password:  "root",
		DialOptions: []grpc.DialOption{
			grpc.WithBlock(),
		},
	})
	if err != nil {
		log.Fatal(err)
	}

	resp, err := client.Get(context.Background(), "test")
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(resp.Kvs)

	time.Sleep(6 * time.Second)

	_, err = client.Get(context.Background(), "test")
	if err != nil {
		log.Fatal(err)
	}
}

Output:

[key:"test" create_revision:2 mod_revision:2 version:1 value:"test" ]
{"level":"warn","ts":"2021-10-11T11:38:59.474+0200","logger":"etcd-client","caller":"v3@v3.5.0/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc0001ef180/#initially=[127.0.0.1:2379]","attempt":0,"error":"rpc error: code = Unauthenticated desc = etcdserver: invalid auth token"}

As you can see, the first client.Get succeeded in fetching the test key, but the second one fails with invalid auth token.

Am I missing something simple here?

EDIT: If you make 10 requests while sleeping for 1 second in-between, the error does not show up.

	for i := 1; i <= 10; i++ {
		time.Sleep(1 * time.Second)
                // no error
		resp, err := client.Get(context.Background(), "test")
		if err != nil {
			log.Fatal(err)
		}

		fmt.Println(resp.Kvs)
	}

	time.Sleep(6 * time.Second)
        // return invalid auth token error
	_, err = client.Get(context.Background(), "test")
	if err != nil {
		log.Fatal(err)
	}