Google API .NET Can't access shared folder files

Question

I'm been trying to do some custom code where I search on a Google Sheet file I owned for a specific string. Right now I have this working, I authenticated using a ApiKey and everything is working fine, BUT!!! I had to change the privacy of the file to "Public with url" to work. I think this is not quite right tho...

Then I moved to the next step, to iterate through all the files on a folder and its sub-folders, and search for that string on all the files, and here is where I'm having problems...

        string ApplicationName = "My App Name";
        string[] Scopes = { DriveService.Scope.Drive, DriveService.Scope.DriveFile };

        // Create Google Sheets API service.
        var service = new DriveService(new BaseClientService.Initializer
        {
            ApplicationName = ApplicationName,
            ApiKey = AppSettings.GetValue(AppSettings.API_KEY)
        });

        String folderId = "folder_id";

        ChildrenResource.ListRequest request = service.Children.List(folderId);

        do
        {
            try
            {
                ChildList children = request.Execute();

                foreach (ChildReference child in children.Items)
                {
                    Console.WriteLine("File Id: " + child.Id);
                }
                request.PageToken = children.NextPageToken;
            }
            catch (Exception e)
            {
                Console.WriteLine("An error occurred: " + e.Message);
                request.PageToken = null;
            }
        } while (!String.IsNullOrEmpty(request.PageToken));

And I'm getting this error:

Google.Apis.Requests.RequestError
Login Required [401]
Errors [
    Message[Login Required] Location[Authorization - header] Reason[required] Domain[global]
]

The same API Key is the one I'm using for the other chunk of code where I check if a single file has a string. The difference and where I think the problem is, is that the folder where I want to iterate the files is shared with me (I'm not the proprietary, but I have full access permissions to it). I also tried changing its privacy to Public without results.

Do you know what I'm getting this error? I have no clue.

SOLUTION:

        string ApplicationName = "My App Name";
        string[] Scopes = { DriveService.Scope.Drive, DriveService.Scope.DriveFile };

        ClientSecrets secrets = new ClientSecrets()
        {
            ClientId = ""MY_CLIENT_ID,
            ClientSecret = "MY_CLIENT_SECRET"
        };

        var token = new TokenResponse
        {
            AccessToken = "MY_ACCESS_TOKEN",
            RefreshToken = "MY_REFRESH_TOKEN"
        };

        var credentials = new UserCredential(new GoogleAuthorizationCodeFlow(
            new GoogleAuthorizationCodeFlow.Initializer
            {
                ClientSecrets = secrets
            }),
            "user",
            token);

        var service = new DriveService(new BaseClientService.Initializer()
        {
            HttpClientInitializer = credentials,
            ApplicationName = ApplicationName
        });

        return service;

All the tokens and keys, I got them from the OAuth2 Playground, is very easy to follow. Also thanks to this other guy answer.

Answer 1

If you haven't done so, try the suggested action for 401: Invalid Credentials error. Refresh the access token using the long-lived refresh token. If this fails, direct the user through the OAuth flow, as described in Authorizing Your App with Google Drive.

Encountered error is usually due to the following:

• Token expiry.
• Token revocation. This would cause both the access token and the refresh token to stop working.
• Token not authorized for needed scopes.
• Request not authorized correctly with OAuth 2.0 protocol.

See Handling errors: revoked or invalid tokens for more information.