Quoting wkirby on Hacker News

Permissions have three moving parts, who wants to do it, what do they want to do, and on what object. Any good permission system has to be able to efficiently answer any permutation of those variables. Given this person and this object, what can they do? Given this object and this action, who can do it? Given this person and this action, which objects can they act upon?

— wkirby on Hacker News

good hacker hackernews moving object permissions person variables