/// <summary>
/// 生成图片验证码
/// </summary>
/// <param name="httpResponse"></param>
/// <param name="guid"></param>
/// <param name="length"></param>
/// <returns></returns>
public static void GenerateImageCode(this HttpResponse httpResponse, string guid, int length = 4)
{
var bytes = VerifyCodeHelper.GenerateImageCode(guid, length);
httpResponse.Headers.Add("Access-Control-Expose-Headers", "X-VGuid");
httpResponse.Headers.Add("X-VGuid", guid);
httpResponse.ContentType = "image/png";
httpResponse.StatusCode = StatusCodes.Status200OK;
httpResponse.Body.WriteAsync(bytes, 0, bytes.Length);
}