Google Docs thumbnail link returns 404 - google-drive-api

Question

I have questions regarding the behavior of the Google Drive v3 API files resource thumbnailLink property for Google Docs files. There are two different types of thumbnail links created depending if the file is a Google Doc or other type of file. When going to the thumbnailLink URL for a Google Doc I always get a 404 response, unless I open it on a Chrome browser where I am logged in with the same Google account.
My questions about the thumbnail link are:
What is the minimum OAuth scope required to access it?
What are the exact criteria required for me to have see the thumbnail image in a browser instead of getting a 404?
Is it possible to make the link to google doc thumbnails publicly accessible?
If not, is there some alternative way to build the thumbnail url?
I preferably want to avoid this answer as it will either expose the access key or add complication by setting up a proxy.
This is the format of the google doc thumbnail link: https://docs.google.com/feeds/vt?gd=true&id=1TjchRkZ0MxurnBkKNitDtoMQiyJUV6rv0z9HQ7kHEg0&v=3&s=AMedNnoAAAAAXaTCgqfi_sjlT4SAGAEd_ZABNBoSvMnM&sz=s220
Other types of documents that use the following type of thumbnail link are publicly available: https://lh3.googleusercontent.com/JkrFnbTt-H1rJb-kXhjRsQI3NiiVu7DYD_L7kBLPvBzu4-ieXNB6Jb-ukQpHwujlzybaeirEyV0=s220
I see this behavior in the Drive v3 "Try This API" screen with all scopes authorized. I go to the thumbnailLink immediately after getting the response so it is not expired.
Edit: The webViewLink works for me in the case of a google slide. So I am allowed to see the full contents publicly using that link but still get a 404 with the thumbnaiLink. Based on that inconsistency this seems like a bug, not a security or permissions issue.

Answer 1

This is not a bug. You are not supposed to be able to access the thumbnailLink if you don't have access to the file's content, as indicated here.
As a workaround, I would propose your app or whoever has access to the thumbnail links to upload the thumbnails to Drive, so that users can access these Drive links. Anyway, I don't know the details of your project so I'm not sure this would be a feasible or desired workaround.

Answer 2

The reason why you are getting a 404 is that the binary documents' thumbnails are publicly accessible. If you can get your hands to the ThumbnailLink field of Google File, you can download the thumbnail images using a simple WebClient without any authentication.
However, if you're trying to download a Google Document's thumbnail image using WebClient that will give you a 404 error, because Google expects that you download this ThumbnailLink URI using an authenticated connection.
I had faced a similar problem and was able to resolve it very easily. I use Google Drive API (version 3) for accessing the documents on Google Drive. The Google API has already authenticated my account which is how I am able to acquire the ThumbnailLink in the first place. But instead of using WebClient, use the DriveService's HTTPClient to download the thumbnail. The HTTPClient in DriveService creates an authenticated HTTP request allowing you to download thumbnails for Google Documents as well.
private async Task<bool> DownloadThumbnail(string thumbnailURL, string localFile)
{
try
{
var client = DriveService.HttpClient;
var response = await client.GetAsync(thumbnailURL);
using (var fs = new FileStream(localFile, FileMode.CreateNew))
await response.Content.CopyToAsync(fs);
return true;
}
catch (Exception ex)
{
// log error
return false;
}
}

Answer 3

Get thumbnail link with scopes drive and drive.readonly
It's private data Token or login required
https://drive.google.com/thumbnail?authuser=0&sz=w280&id=[fileid]
sz = size
w = width