如何使用web客户端访问安全url

我试图通过web客户端访问安全的url，并得到一些错误。总的目的是从安全的url下载图像..

请注意，早些时候，我能够使用http从存储库下载图像，现在他们在同一url中强制执行(安全)https。我们有一个控制台应用程序，它定期运行，从服务器提取图像并存储在本地。

请告诉我我做错了什么?或者缺少什么?

以下是我所面临的问题。

1. ///如果我使用代码节1…我得到错误说参数无效。
2. ///如果我使用代码节2…文件被保存到本地，但得到一个消息"文件似乎损坏或大，无法打开。

第1节和第2节列在下面。

            using (WebClient webClient = new WebClient())
            {
                webClient.Headers.Add("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)");
                webClient.Credentials = new NetworkCredential("id", "pwd");  // if credentials are wrong...still I get the imageByte
                /// section 1 - if I use this code... I get error saying Parameter is not valid.
                // ----------------------------- Start --------------------------------
                imageByte = webClient.DownloadData("https://someurl/source/abcd.jpeg");
                ////Initialize image variable
                Image newImage;
                ////Read image data into a memory stream
                using (MemoryStream ms = new MemoryStream(imageByte, 0, imageByte.Length, true))
                {
                    ms.Write(imageByte, 0, imageByte.Length);
                    //Set image variable value using memory stream.
                    newImage = Image.FromStream(ms, true, false); // Throws error at this line saying that parameter is not valid.
                }
                newImage.Save(@"location'image.jpeg");
                // ----------------------------- End --------------------------------

                /// section 2 - if I use this code... File gets saved to local but get a message " File appear to be corrupt or large and not able to open.
                // ----------------------------- Start --------------------------------
                webClient.DownloadFile("https://someurl/source/abcd.jpeg", @"location'image.jpeg");
                // ----------------------------- End --------------------------------
            } 

// Obtain the WebHeaderCollection instance containing the header name/value pair from the response.
WebHeaderCollection myWebHeaderCollection = myWebClient.ResponseHeaders;
Console.WriteLine("'nDisplaying the response headers'n");
// Loop through the ResponseHeaders and display the header name/value pairs.
for (int i=0; i < myWebHeaderCollection.Count; i++)
{       
    Console.WriteLine ("'t" + myWebHeaderCollection.GetKey(i) + " = " + myWebHeaderCollection.Get(i));
}