What is a high level approach to creating a software licence server?

Question

I'm on the process of creating a basic CMS, and would like to distribute keys or licences to clients that want to use the software (subscription based service, think Adobe).

The app will be small-scale at first, so I don't think I need to implement any PKI to protect the distribution of the key/licence from MITM/eavesdropping attacks.

I haven't done something like this before, so what can be a high level overview or checklist of things I need to succeed developing this?

I know the question is too broad but I can't wrap my head around this concept so I'd need some help. Thanks.