public async Task <IActionResult> Code() { string code = $"{Thread.CurrentThread.ManagedThreadId} {DateTime.Now.Millisecond:D4}"; CaptchaItem item = new CaptchaItem() { Code = code, SessionId = Guid.NewGuid() }; byte[] buf = await _captchaService.CreateImageAsync(item); Response.Headers.Add("Session", $"{item.SessionId}"); return(File(buf, "image/png")); }