private async Task <string> GetAccessTokenAsync()
{
string accessToken = tokenResponse?.GetValidAccessToken();
if (string.IsNullOrEmpty(accessToken))
{
lock (accessTokenTaskLock)
{
if (accessTokenTask == null)
{
// access token task may be shared by multiple messaging task, thus should not pass cancellationToken to it
accessTokenTask = RequestAccessTokenAsync(default);
