ItextSharp（XMLWorkerHelper ParseXHtml）没有使用Https url加载图像

Question

我有一个应该生成pdf的网站。 图像的URL由Web服务提供。 网址包含https，不上传我的pdf。

我该如何解决这个问题？

 iTextSharp.text.Document doc = new iTextSharp.text.Document(iTextSharp.text.PageSize.A4, 0, 0, 0, 0);

        var html = string.Format(@"{0}", htmlToConvert);
        StringReader strReader = new StringReader(html);
        System.IO.MemoryStream m = new System.IO.MemoryStream();

        var pdfWriter = PdfWriter.GetInstance(doc, m);           
        doc.Open();           
        iTextSharp.tool.xml.XMLWorkerHelper.GetInstance().ParseXHtml(pdfWriter, doc, strReader);           
        doc.Close();           
        pdfWriter.Flush();
        pdfWriter.Close();

        HttpResponseBase response = context.HttpContext.Response;
        response.Clear();
        // add the Content-Type and Content-Disposition HTTP headers
        response.AddHeader("Content-Type", "application/pdf");
        response.AddHeader("Content-Disposition", String.Format("attachment; filename=file.pdf; size={0}", m.GetBuffer().Length.ToString()));           
        response.OutputStream.Write(m.GetBuffer(), 0, m.GetBuffer().Length);
        response.OutputStream.Flush();
        response.OutputStream.Close();
        response.End();