Comment by black_knight

2 days ago

> can this subject perform this action on this object?

IMHO, the most elegant method to answer this question is capability based access control. If the subject can utter the action, then it can perform it. And then delegation is the transfer of nouns and verbs to perform the utterances.

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black_knight

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fmajid  17 hours ago

Even that is oversimplified. To launch nuclear-armed ICBMs, it takes to subjects to turn two keys separated by sufficient distance that no one person can turn both keys at the same time. In many cases, specially involving sysadmins, you want a quorum so a rogue sysadmin cannot lock others out or commit other destructive actions.

simiones  2 days ago

> If the subject can utter the action, then it can perform it.

This sounds like another layer of weird terminology that doesn't mean anything for someone who is not familiar with whatever capability system you're thinking of.

Say I am a user who can see a particular directory on a shared setup. I try to upload a file in this directory, using the same method that worked on another directory. The question of AuthZ is: will I be allowed to do it or not? In the plain sense of the words, I can absolutely "utter the action", I have all of the "verbs" (upload) and "nouns" (the file, the destination path). Still, I should not be allowed to perform the action if I was only given read-only access here.

Now sure, you can say that "upload to dirA" is a different verb than "upload to dirB". But this is just confusing terminology, it doesn't enlighten anything.

  • black_knight  2 days ago

    You seem to understand it just fine.

    Your accessor, dirB, should not contain the “upload files” verb, while your dirA accessor (noun) should.

    My favorite example is the home directory and the file picker. Why should a program have access to all your files by default then politely ask you which file it should read/write to? It would make more sense if the file picker was something the operating system ran when a program wants to edit a file, and what came back to the program after you selected was the accessor for that file (with read and/or write verbs).

    So the program only have access to those files you have it access to. It cannot even ask the question to open another file, because it only has opaque accessors to those files it has been given.

    • uncommoncense  2 days ago

      What you're describing is essentially what the authorization system would need to do in order to answer the question "can this subject perform this action on this object?". If you're suggesting that the program should receive a list a priori, then there are potential scale issues since that list would need to be exhaustive of both nouns and verbs, which can be a large set.

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    • nmadden  2 days ago

      I used to use the example of Dropbox’s chooser API to illustrate this: https://www.dropbox.com/developers/chooser

      If you use this API (via a simple widget library) then the user simply picks a file in their dropbox and the app gets access to that one file. Vs OAuth where you grant the app broad access to the whole dropbox (or maybe some sub-folder).

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    • simiones  2 days ago

      First of all, this necessitates a certain data model, where instead of a "UploadFile(file, destPath)" operation, I have to have a "destPath.UploadFile(file)" operation. This would be ok for this case, but not all operations can be expressed in this simple parent -> child relationship.

      Furthermore, even here, this doesn't cover another case: what if I am allowed to add files to destPath, but I'm not allowed to modify a specific file? This API still has to fail if `destPath/file.Name` already exists and I'm not allowed to modify it (or it at least has to do something different than when `destPath/file.Name` doesn't already exist).

      And even if we accept that we can only ever write things in this way, this still leaves the problem of terminology intact. Depending on the technology, it's simply not true that I can't "utter this phrase" if I don't have the capability. For example, if this is an HTTP API, then I can always do a `POST /dest-path/upload-file` with the file I want, regardless of whether I have the authorization to access that or not. Sure, if it's a HATEOAS-style API, the `GET /dest-path` might not return a link to `./upload-file` at all, but that doesn't mean that I can't utter that sentence - i.e. issue that HTTP request.

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williamdclt  2 days ago

I have more experience with authorization than most engineers, even engineers who have some experience with authn/authz, and I have no idea what that "subject can utter the action" or "transfer of nouns and verbs to perform the utterances" could mean

  • formerly_proven  2 days ago

    They clearly mean capabilities.

    https://en.wikipedia.org/wiki/Capability-based_security

    > Capabilities achieve their objective of improving system security by being used in place of forgeable references. A forgeable reference (for example, a path name) identifies an object, but does not specify which access rights are appropriate for that object and the user program which holds that reference. Consequently, any attempt to access the referenced object must be validated by the operating system, based on the ambient authority of the requesting program, typically via the use of an access-control list (ACL).

    > Instead, in a system with capabilities, the mere fact that a user program possesses that capability entitles it to use the referenced object in accordance with the rights that are specified by that capability. In theory, a system with capabilities removes the need for any access control list or similar mechanism by giving all entities all and only the capabilities they will actually need.

  • black_knight  2 days ago

    I chose those words here because they are not programming language specific. For the OOPers, I guess you can imagine I said “objects” and “methods”.

    • williamdclt  2 days ago

      Not particularly an OOPer, but regardless tou're only making it less clear I'm afraid! "objects" and "methods" instead of what?

      I'll make an educated guess that you mean "objects and methods" instead of "subject and action" or "noun and verb" respectively. But it's really the "utter" and "transfer" terminology that I have no idea what it might mean

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