OAuth2 is always confusing to me even though I've implemented it a few times. I learn it and then quickly forget the details so I always have to re-learn it. I was worried about doing it in Google Apps Script since that adds an extra layer of stuff on top of it all. Fortunately, I found an excellent library on GitHub and I've already added GitHub and Google Analytics (with many more planned). As far as I know, Data Connector is the only Sheets Add-on of it's kind that lets you have OAuth2 connections on the free tier. Our competitors either make you pay for it or don't offer it at all.