public Task <string> AcquireLeaseAsync(TimeSpan?leaseTime, string proposedLeaseId,
                                               CancellationToken cancellationToken)
        {
            if (proposedLeaseId != null)
            {
                throw new NotImplementedException();
            }

            string leaseId = _store.AcquireLease(_containerName, _blobName, leaseTime);

            return(Task.FromResult(leaseId));
        }