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Comment by closeparen | Hacker News Reader

As a practical matter in an enterprise use case, you really want to be able to tell the user why their request is denied and what they can do about it. One thing I really appreciate at my employer is that any "access denied" message provides an on-ramp to the process of either amending my request to something that's within my permissions, or else getting the requisite approvals.

How do you get this kind of explainability when the authorization decision involves such advanced magic as logic programming languages?

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>> How do you get this kind of explainability when the authorization decision involves such advanced magic as logic programming languages?

You could do this by generating a trace of the execution of the logic program, as you run the program. For example you can write:

  allow(update, Resource, User, Reason):- 
    Reason = owner(Resource, User)
   ,Reason.

Although that is probably not very idiomatic datalog. That is, I don't know if you can "call" a literal bound to a variable like I do in the last line of the program by declaring "Reason" after binding Reason to "owner(Resource, User)". If you do that in Prolog, the Prolog engine will prove the literal bound to "Reason" and execute the "owner" program. I don't know if that works in datalog. You can of course do all this without call-magic:

  allow(update, Resource, User, Reason):- 
     owner(Resource, User)
    ,Reason = owner(Resource, User).

Historically, mechanisms of explanation very similar to the one above were common in expert systems of old, at least the ones implemented in Prolog. There used to be a nice free e-book describing how to build expert systems in Prolog in a quick-and-dirty fashion, but I can't find it online anymore. There's this book by Amzi Prolog though:

https://amzi.com/distribution/files/xsip_book.pdf

And this has a section on "Explanation" that describes a tracing mechanism based on the classic box-model debugger of Prolog engines. The technique can be applied to datalog and the program doesn't have to be an expert system, just to make it clear.

I think security systems tend to tell as little as possible in these cases because to do otherwise reveals something of the internal structure of a system, potentially indicating vulnerable points.

IIRC a post on naming servers where someone said if they knew one server was called Bilbo then they had a pretty good idea what the other servers might be named after. Seemed a good point.

This seems misguided. If you are taking principle-of-least-privilege seriously (and it seems that's what people are trying to do with very sophisticated authz systems) then legitimate users will bounce off the edges of their privileges very frequently. If they can't figure out what those edges are or how to expand the frontier when necessary, they're not going to be able to accomplish necessary tasks.

A policy of "stay the hell away, don't even ask" only works if you're drawing the boundary very far from the user's legitimate sphere of influence.

Dunno, just reporting what I understood to be. It may be a distinction can be made between company-internal and company-external attempts at access, but that is pretty risky.

Any solution to the valid point you have made would have to be organisational.

But the saying goes something like "security annoying, good security is very annoying" - anyone know the original?

This is definitely a consideration for authorization. To do it well you need to be able to distinguish when you want to reveal information.

For example, our APIs push people towards returning a 404 if the user doesn't have read access (you shouldn't even know it exists!), but a 403 if you can read but not edit.

You would probably want to do similar here -- only return a reason if the user is allowed to know it exists, but they don't have access. (e.g. it might be "read_exist" vs "read_details" -> "you cannot read the details of this document because you are not a member of this folder".)

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