But folks really cache auth related data? Isn’t that better handled purely through client <> server requests and handling caching for all UI or action based data?
Not at scale. If our auth caching stops, our auth servers can get overloaded at peak times. Granted, horizontal scaling auth is a better first round choice, but caching gives you vertical scaling when you are hitting limits on your database. Another option is z-scaling, but that is really just a way to improve either of the previous two (have different pools of user databases).