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One thing we could do is:

- Return Forbidden or NotFound if we can determine the correct answer
- When we can't (i.e. the object doesn't exist), then return NotFound unless a new config value 'policy_harden' (?) is set to true (default false) in which case we translate NotFound into Forbidden.

Henry
On 23 Jul 2013, at 18:31, Adam Young wrote:

> On 07/23/2013 12:54 PM, David Chadwick wrote:
>> When writing a previous ISO standard the approach we took was as follows 
>> 
>> Lie to people who are not authorised. 
> 
> Is that your verbage?  I am going to reuse that quote, and I would like to get the attribution correct.
> 
>> 
>> So applying this approach to your situation, you could reply Not Found to people who are authorised to see the object if it had existed but does not, and Not Found to those not authorised to see it, regardless of whether it exists or not. In this case, only those who are authorised to see the object will get it if it exists. Those not authorised cannot tell the difference between objects that dont exist and those that do exist 
> 
> So, to try and apply this to a semi-real example:  There are two types of URLs.  Ones that are like this:
> 
> users/55FEEDBABECAFE
> 
> and ones like this:
> 
> domain/66DEADBEEF0000/users/55FEEDBABECAFE
> 
> 
> In the first case, you are selecting against a global collection, and in the second, against a scoped collection.
> 
> For unscoped, you have to treat all users as equal, and thus a 404 probably makes sense.
> 
> For a scoped collection we could return a 404 or a 403 Forbidden based on the users credentials:  all resources under domain/66DEADBEEF0000  would show up as 403s regardless of existantce or not if the user had no roles in the domain 66DEADBEEF0000.  A user that would be allowed access to resources in 66DEADBEEF0000  would get a 403 only for an object that existed but that they had no permission to read, and 404 for a resource that doesn't exist.
> 
> 
> 
> 
>> 
>> regards 
>> 
>> David 
>> 
>> 
>> On 23/07/2013 16:40, Henry Nash wrote: 
>>> Hi 
>>> 
>>> As part of bp https://blueprints.launchpad.net/keystone/+spec/policy-on-api-target I have uploaded some example WIP code showing a proposed approach for just a few API calls (one easy, one more complex).  I'd appreciate early feedback on this before I take it any further. 
>>> 
>>> https://review.openstack.org/#/c/38308/ 
>>> 
>>> A couple of points: 
>>> 
>>> - One question is on how to handle errors when you are going to get a target object before doing you policy check.  What do you do if the object does not exist?  If you return NotFound, then someone, who was not authorized  could troll for the existence of entities by seeing whether they got NotFound or Forbidden.  If however, you return Forbidden, then users who are authorized to, say, manage users in a domain would aways get Forbidden for objects that didn't exist (since we can know where the non-existant object was!).  So this would modify the expected return codes. 
>>> 
>>> - I really think we need some good documentation on how to bud keystone policy files.  I'm happy to take a first cut as such a thing - what do you think the right place is for such documentation 
>>> 
>>> _______________________________________________ 
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>>> OpenStack-dev at lists.openstack.org 
>>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev 
>>> 
>> 
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> 
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