Most of the comments on this page are referring to authentication. It's important to know, but also the piece you're likely to spend far less time on. It's where most of the heavy lifting will be done by some vendor or tool you set up instead of by your own code.
Authorization is far less likely to be something you get off the shelf and far more likely to be where you spend significant time. It can be very intimately connected to your business logic. Active Directory roles and groups are one authorization solution for a particular class of problems but I have only seen them used for controlling business internal assets (mostly file servers); not public-facing applications.
I really like Oso Academy as a resource for authorization topics. It's structured like a progressive course, though I don't know if they have the kind of exercises you mentioned.