Easiest way to create an online userbase

Question

I wasn't sure how to word this, so hopefully I get the point across alright. Basically, I am planning on releasing this program, and I want it to be a subscription based payment. So I want to force everyone to login, and I want to be able to control the accounts in the database that it is checking so that I can remove an account if their subscription is over and they haven't paid. This program was done in Visual Studio using Windows Forms and obviously c#. I've tossed around a ton of ways to do this in my head, but I really can't think of the best / easiest way. There won't be a massive number of users. I've thought about using googles api to use sheets or download a file from drive every time, but I don't think that either of those would work as they would have to be signed into my google account? Hopefully someone has a good idea for this. Thanks.