Accessing Google Sheets with C# after the Google client login shut down is not as easy as you might think. The problem is that the Google Sheets is part of the old Gdata api and becouse of that you have to use the Gdata library to access it. The current Google .net client library which supports Oauth2 and Service accounts only supports the newer discovery APIs. That doesnt mean that it cant be done it just means that you need to merge two diffrent client librarys in the same project to get it to work.
This tutorial is not complte it is a work in progress, please come with feed back so that we can improve it.
You will need the NuGet packages from both client libraries. The first one is the current Google .net client library which we need to authentcate. The second is the old Gdata library which we use to access Google SpreadSheets.
Again this is a work in progress I will fix this as I get it working. It should be possible to use OAuth2 and a public API key as well I just haven’t had time to get it working. This should give you a head start if you are like me trying to access Google Sheets with C#.