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From Angela Schreiber <anch...@adobe.com>
Subject Re: How does Jackrabbit resolve ACL permissions?
Date Wed, 13 Feb 2013 12:29:53 GMT
hi marian

imo there shouldn't be any major obstacles in setting up the
ACL to reflect the permissions as you describe below.
in quickly tried it out on the crx-explorer using the following

- groupA
- groupB

- userA: member of groupA (and everyone)
- userB: member of groupB (and everyone)
- userC: member of groupA and groupB (and everyone)

acl setup
+ root
   + a
     + rep:policy
       + allow
         - jcr:primaryType = rep:GrantACE
         - rep:principalName = groupA
         - rep:privileges = [jcr:read]
   + b
     + rep:policy
       + allow
         - jcr:primaryType = rep:DenyACE
         - rep:principalName = groupB
         - rep:privileges = [jcr:read]


- userA can read /a but not /b
- userB can read /b but not /a
- userC can read /a and /b

additional adding an DENY ace for everyone on the root is
redundant and doesn't not have an effect on the result.

general notes

- ACEs are inherited through the node hierarchy. ACEs defined on
   a particular node take precedence over inherited onces.
   defining addition restrictions may be used to limit the effect to
   certain parts of the subtree defined by the access controlled node

- as long as ACEs are defined from group principals the evaluation
   is strictly hierarchical. on a single ACL the order of ACEs matters.

- if you define ACEs for non-group principal they will take predecence
   in any case: over the group principals and over the inheritance rule
   defined above.

regarding your comments below:

1) that works for me... see above. in don't think you analysis
    matches the way the permissions are evaluated.
2) that would work as well but the ACE for everyone is redundant.
    it would not work if you would allow group A first and deny everyone
    group after that... as the ACE for A would become redundant.

hope that helps

On 2/13/13 11:34 AM, SCHEDENIG Marian wrote:
> Hi,
> we’re using the standard ACLProvider for permission handling. We’re now
> running into problems when trying to set up slightly more complex ACLs
> than we’ve used so far:
> Say we have three groups, “everyone” (which is Jackrabbit’s
> EveryonePrincipal) and “A” and “B”. We want to allow only users in the A
> group to be able to access the folder /a_folder and only members of B to
> access /b_folder. A user may be a member of A, B, A and B or of neither
> group. If user X is a member of A and not a member of B, X should still
> have access to /a_folder.
> We’ve tried two approaches:
> 1. Deny full permissions to “everyone” on the root folder and then grant
> full permissions to A on /a_folder and to B on /b_folder. This fails,
> apparently because permissions are resolved in a “top down” manner, and
> as soon as it has been established that a user doesn’t have access to a
> parent folder, its subfolders are no longer evaluated. That’s fine, if
> we can find a different way to do it.
> 2. Deny full permissions to “everyone” on /a_folder and grant full
> permissions to A on the same folder (and the same with “everyone” and B
> on /b_folder). This also fails, although apparently it works for user X
> if we deny “everyone” and grant X (specifically the user) on the folder.
> I’m now wondering: How exactly does Jackrabbit resolve permissions? Case
> 1 seems to be clear, but what are the exact rules for overlapping grants
> and denies on the same resource? And what is the correct way to solve
> our requirement?
> Thanks,
> Marian.
> --
> *DI Marian Schedenig*
> Senior Developer
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