public IHttpActionResult AttachStream(string streamId, string toStreamId, DateTime? expiresAt = null)
{
if (expiresAt.HasValue == false)
expiresAt = DateTime.FromFileTimeUtc(ActivityStream.DefaultExpirationTimestamp);
var streamIdBytes = Encoding.UTF8.GetBytes(streamId);
var toStreamIdBytes = Encoding.UTF8.GetBytes(toStreamId);
WebApiApplication.StreamService.Attach(toStreamIdBytes, streamIdBytes, expiresAt.Value);
return Ok();
}