Download embedded images from google document - google-api

Question

I'm trying to download embedded images in a google document using their Drive API and WebClient. A few of the images works just fine, and that is pure images. The others responds with a redirect to the login page instead of the file, so i suppose it has something to do with the credentials (I'm not setting any credetials to my WebClient right now). The images that fail looks like they are called drawings instead of images. Can that be the issue here?
The links that breaks looks like this:
https://docs.google.com/a/irissystem.se/drawings/image?id=HERE_IS_AN_UNIQUE_ID&rev=1&h=81&w=28&ac=1
Is there a way to download images like this using the HttpClient of DriveService-class or a way to apply my credentials from my DriveService to my WebClient instance?
The code below is used to parse the document and download the images.
foreach (HtmlNode img in doc.DocumentNode.SelectNodes("//img")) {
HtmlAttribute src = img.Attributes["src"];
using (WebClient webClient = new WebClient()) {
byte[] data = webClient.DownloadData(src.Value);
using (MemoryStream imagestream = new MemoryStream(data)) {
byte[] imagebinary = imagestream.ToArray();
Images.Add(src.Value, imagebinary);
}
}
}
UPDATE
Thanks to the comment below, i started thinking about the HttpClient and download stream and it turned out to be a good solution. The code below uses my Google DataService (authenticated and done) to download the embedded file as a stream. This works for both drawings and images, so it is a all round solution.
public byte[] GetFileByUrl(string Url, string ExportType = "text/plain") {
var stream = Service.HttpClient.GetStreamAsync(Url);
var result = stream.Result;
using (System.IO.MemoryStream ms = new System.IO.MemoryStream()) {
result.CopyTo(ms);
return ms.ToArray();
}
}
The code for auth looks like this
ServiceAccountCredential credential = new ServiceAccountCredential(
new ServiceAccountCredential.Initializer(SERVICE_ACCOUNT_EMAIL)
{
User = "xxx#xxx.com",
Scopes = new[] { DriveService.Scope.Drive }
}.FromCertificate(certificate));
Service = new DriveService(new BaseClientService.Initializer()
{
HttpClientInitializer = credential,
ApplicationName = "xxx",
});