Unauthorized response when downloading file with Service Account in Google Drive API

Question

I'm using the following code to get credentials from Google's Authentication server in order to access the Google drive API

 public static Google.Apis.Services.BaseClientService.Initializer getCredentials()
    {

        String serviceAccountEmail = "[email protected]";

        var certificate = new X509Certificate2(@"xxx.p12", "notasecret", X509KeyStorageFlags.Exportable);

        ServiceAccountCredential credential = new ServiceAccountCredential(
           new ServiceAccountCredential.Initializer(serviceAccountEmail)
           {
               Scopes = new[] { DriveService.Scope.Drive }
           }.FromCertificate(certificate));



        return new BaseClientService.Initializer()
        {
            HttpClientInitializer = credential,
            ApplicationName = "AppName",
        };



    }

then retrieving the Download url from the file metadata and attempting to download that file with the following code:

 public static System.IO.Stream DownloadFile(Google.Apis.Drive.v2.Data.File file, Google.Apis.Drive.v2.DriveService service)
   {



       if (!String.IsNullOrEmpty(file.DownloadUrl))
       {
           try
           {
               HttpWebRequest request = (HttpWebRequest)WebRequest.Create(
                   new Uri(file.DownloadUrl));
              // authenticator.ApplyAuthenticationToRequest(request);
               HttpWebResponse response = (HttpWebResponse)request.GetResponse();
               if (response.StatusCode == HttpStatusCode.OK)
               {
                   return response.GetResponseStream();
               }
               else
               {
                   Console.WriteLine(
                       "An error occurred: " + response.StatusDescription);
                   return null;
               }
           }
           catch (Exception e)
           {
               Console.WriteLine("An error occurred: " + e.Message);
               return null;
           }
       }
       else
       {
           // The file doesn't have any content stored on Drive.
           return null;
       }
   }

However I'm receiving a 401 unauthorized response. I'm assuming I need to add an Authorization header in the request along the lines of Authorization: Bearer {ACCESS_TOKEN} but the HttpClientInitializer.Token property is null. Is it possible to authenticate this Request using the ServiceAccountCredential?

Answer 1

I faced the same problem today. Using your approach to make a request no Authentication header is provided. I needed to construct the request a bit differently. Where you have:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(
               new Uri(file.DownloadUrl));

You should have:

HttpResponseMessage response = await service.HttpClient.GetAsync(new Uri(file.DownloadUrl));

This ensures that the request is properly authenticated.

Answer 2

Your code is off a little. I don't have a service account Google Drive API example right this minute. This is one for Big Query its almost the same.

String serviceAccountEmail = "539621478854-imkdv94bgujcom228h3ea33kmkoefhil@developer.gserviceaccount.com";
var certificate = new X509Certificate2(@"C:\Users\linda_l\Documents\GitHub\GoogleBigQueryServiceAccount\GoogleBigQueryServiceAccount\key.p12", "notasecret", X509KeyStorageFlags.Exportable);

ServiceAccountCredential credential = new ServiceAccountCredential(
       new ServiceAccountCredential.Initializer(serviceAccountEmail)
          {
           Scopes = new[] { BigqueryService.Scope.DevstorageReadOnly }
          }.FromCertificate(certificate));

        // Create the service.
var service = new BigqueryService(new BaseClientService.Initializer()
      {
       HttpClientInitializer = credential,
       ApplicationName = "BigQuery API Sample",
       });

Can you see where the BaseClientService.Initializer() is used to create the BigqueryService. I think you need to create a GoogleDriveService. Once you have created the service you should be able to use the service to download the file. You shouldn't need to be doing it though a HTTPRequest.

I will see if i can find a better example tonight using Google Drive.