Need a login/account system so clients can access the rest of the application

So this project has multiple parts but would be based on a subscription, so a way is needed for those who stop subscribing to no longer have access to the application. It's really a group of apps who all work in tandem, so basically this login thing needs to be the "keys to the castle". It needs to work by connecting to a database of users, probably by their email. Passwords would need to be added and then updated in that same database. Preferably the database/client login would communicate once per day to make sure that the subscription is active, and once it is deemed inactive the program would be able to prevent access to other features. Furthermore, a simple check to make sure that the account is only active on one system would be necessary. Deliverables Networking is a mystery to me no matter how much I read up on it. What I am asking does not seem to hard though. A very barebones login screen that really only verifies the user is active and allows them to access the other apps that are included in the application. It just has to communicate with an external database of accounts, which could just be a server in my room.