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"));
}