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On 07/22/2014 11:00 PM, Nathan Kinder wrote:
> 
> 
> On 07/22/2014 06:55 PM, Steven Hardy wrote:
>> On Tue, Jul 22, 2014 at 05:20:44PM -0700, Nathan Kinder wrote:
>>> Hi,
>>>
>>> I've had a few discussions recently related to Keystone trusts with
>>> regards to imposing restrictions on trusts at a deployment level.
>>> Currently, the creator of a trust is able to specify the following
>>> restrictions on the trust at creation time:
>>>
>>>   - an expiration time for the trust
>>>   - the number of times that the trust can be used to issue trust tokens
>>>
>>> If an expiration time (expires_at) is not specified by the creator of
>>> the trust, then it never expires.  Similarly, if the number of uses
>>> (remaining_uses) is not specified by the creator of the trust, it has an
>>> unlimited number of uses.  The important thing to note is that the
>>> restrictions are entirely in the control of the trust creator.
>>>
>>> There may be cases where a particular deployment wants to specify global
>>> maximum values for these restrictions to prevent a trust from being
>>> granted indefinitely.  For example, Keystone configuration could specify
>>> that a trust can't be created that has >100 remaining uses or is valid
>>> for more than 6 months.  This would certainly cause problems for some
>>> deployments that may be relying on indefinite trusts, but it is also a
>>> nice security control for deployments that don't want to allow something
>>> so open-ended.
>>>
>>> I'm wondering about the feasibility of this sort of change, particularly
>>> from an API compatibility perspective.  An attempt to create a trust
>>> without an expires_at value should still be considered as an attempt to
>>> create a trust that never expires, but Keystone could return a '403
>>> Forbidden' response if this request violates the maximum specified in
>>> configuration (this would be similar for remaining_uses).  The semantics
>>> of the API remain the same, but the response has the potential to be
>>> rejected for new reasons.  Is this considered as an API change, or would
>>> this be considered to be OK to implement in the v3 API?  The existing
>>> API docs [1][2] don't really go to this level of detail with regards to
>>> when exactly a 403 will be returned for trust creation, though I know of
>>> specific cases where this response is returned for the create-trust request.
>>
>> FWIW if you start enforcing either of these restrictions by default, you
>> will break heat, and every other delegation-to-a-service use case I'm aware
>> of, where you simply don't have any idea how long the lifetime of the thing
>> created by the service (e.g heat stack, Solum application definition,
>> Mistral workflow or whatever) will be.
>>
>> So while I can understand the desire to make this configurable for some
>> environments, please leave the defaults as the current behavior and be
>> aware that adding these kind of restrictions won't work for many existing
>> trusts use-cases.
> 
> I fully agree.  In no way should the default behavior change.
> 
>>
>> Maybe the solution would be some sort of policy defined exception to these
>> limits?  E.g when delegating to a user in the service project, they do not
>> apply?
> 
> Role-based limits seem to be a natural progression of the idea, though I
> didn't want to throw that out there from the get-go.

I was concerned about this idea from an API compatibility perspective,
but I think the way you have laid it out here makes sense.  Like both
you and Steven said, the behavior of the API when the parameter is not
specified should *not* change.  However, allowing deployment-specific
policy that would reject the request seems fine.

Thanks,

-- 
Russell Bryant