Re: [xacml] Any kind of policies in a request

["Rich.Levinson" <rich.levinson@oracle.com>]

Hi David,

If this is the case, then the course I would recommend is to specify 
what is missing from XACML that is required to meet the requirements for 
those use cases, and then that can be considered as an enhancement.

In general, my opinion is that XACML should be regarded as an 
abstraction, which is intended to be a superset of all possible authz 
policies.

However, as you indicate there always will be some "next requirement", 
and there should be mechanism to carry the policies in a parallel 
channel to the xacml policies, which will enable them to be delivered to 
non-xacml PDPs that are capable of receiving and processing them.

The original proposal I saw was in this email that was discussed at the 
TC meeting a few weeks ago:
http://lists.oasis-open.org/archives/xacml/200911/msg00023.html

which proposed an extension to PolicySet, which would effectively 
intermingle xacml and non-xacml policies within PolicySets, which is 
what I think people were saying was not desirable.

As Hal has suggested, adding the capability to the SAML/XACML decision 
request protocol, possibly allowing non-xacml policies in 
xacml-saml:ReferencePolicies, would address this requirement.
http://lists.oasis-open.org/archives/xacml/200912/msg00053.html

    Thanks,
    Rich


David Chadwick wrote:
> Hi Rich
>
> Rich.Levinson wrote:
>> Hi David,
>>
>> Here are my 4 answers to the questions:
>>
>>     i) there should be a general mechanism for querying any remote PDP
>>     for an authz response Y/N
>>
>>         Y, but xacml req/rsp syntax must be mapped to local syntax of
>>         non-xacml PDPs
>
> obviously. This is what we do already.
>
>>
>>
>>     ii) there is a need to dynamically push a policy to a remote PDP
>>     along with an authz decision request Y/N
>>
>>         Y, but the policy is a xacml policy and if the remote PDP is
>>         non-xacml then there must be a mechanism to map the xacml
>>         policies on arrival to the syntactic reqts of the non-xacml PDP
>
>
> Unfortunately this is not possible since XACML is not a superset of 
> all possible authz policies. It XACML were a superset then you could 
> map from XACML into anything else. But how do you encode a Separation 
> of Duties policy into XACML? How do you encode a behavioural trust 
> policy into XACML?
>
>
>>
>>
>>     iii) the v2 XACML request/response context can be used as a general
>>     purpose mechanism for making an authz query to any ABAC PDP Y/N
>>
>>         Y, but someone must provide a means to map from the XACML
>>         request/response context to the specific ABAC PDP syntax.
>
> agreed. We already do this in our PDP context handler.
>
>>
>>
>>     iv) the SAMLv2 profile of XACML can be used as a general purpose
>>     mechanism for pushing a policy to a remote PDP along with making an
>>     authz query Y/N
>>
>>         Y, but the policies must be XACML policies and if the PDPs are
>>         not XACML PDPs then a mechanism must be provided to map from the
>>         XACML to the non-XACML syntax.
>
> again this wont work for the reasons explained above.
>
> (To use an analogy, its a bit like saying that in the 1980s, SMTP 
> should have been used to carry all the X.400 features and then map 
> from SMTP into X.400. Clearly it was not possible, which is why MIME 
> was invented).
>
>
>>
>> The rationale behind all these answers is that the purpose of this TC 
>> is to define a standard for authorization policies and provide 
>> guidance for developing bindings and provide some bindings to this 
>> standard.
>
> understood
>
>>
>> So, if the issue is that there are non-XACML policies that need to 
>> transmitted in the SAML 2.0 Profile of XACML, my recommendation is 
>> that a binding be developed that specifies how to map these non-xacml 
>> policies to and from XACML Policy format. That way any policy, xacml 
>> or non-xacml, should be able to be sent to any PDP using the SAML 2.0 
>> Profile as is.
>
> Unfortunately your assumption is that any authz policy can be written 
> in  XACML, and I dont think that is the case (e.g. why was XACMLv3 
> developed, because you knew there were policies that could not be 
> expressed in v2, such as delegation. I believe this is still the case 
> for XACMLv3).
>
>
> regards
>
> David
>
>
>>
>>     Thanks,
>>     Rich
>>
>>
>> David Chadwick wrote:
>>> Hi Hal
>>>
>>> Yes indeed this was my original proposal, but the group seemed to 
>>> have some resistance to this encoding, so it was switched to putting 
>>> it into the SAML-XACML request message.
>>>
>>> When deciding about topics such as this, I think it is best to first 
>>> agree on the concept, and only then to agree about the actual syntax 
>>> to be used since several different syntaxes can be used to carry the 
>>> same conceptual entity.
>>>
>>> I am not sure how many people in the XACML group have agreed to the 
>>> concept and therefore will disagree with any syntax changes that are 
>>> proposed, and how many have agreed to the concept but not to the 
>>> syntax.
>>>
>>> I would therefore like to see if we can first get a broad consensus 
>>> on the concept and only then decide which syntax is the most 
>>> appropriate one to carry new policies to PDP.
>>>
>>> So the I should like to ask the group if there is broad consensus 
>>> that a PEP should be able to dynamically send a policy to its PDP 
>>> along with an authz decision request, and if anyone disagrees to say 
>>> why they disagree.
>>>
>>> In a previous message I asked Anil 4 questions about this issue, but 
>>> now I would like to open this up to the whole group to ask if 
>>> everyone could answer these 4 questions privately, and if anyone 
>>> answers No to any of them to give their rationale to the group. We 
>>> can then debate the concept and resolve this issue first before 
>>> proceeding to any syntax encoding details.
>>>
>>> i) there should be a general mechanism for querying any remote PDP 
>>> for an authz response Y/N
>>>
>>> ii) there is a need to dynamically push a policy to a remote PDP 
>>> along with an authz decision request Y/N
>>>
>>> iii) the v2 XACML request/response context can be used as a general 
>>> purpose mechanism for making an authz query to any ABAC PDP Y/N
>>>
>>> iv) the SAMLv2 profile of XACML can be used as a general purpose 
>>> mechanism for pushing a policy to a remote PDP along with making an 
>>> authz query Y/N
>>>
>>> regards
>>>
>>> David
>>>
>>> Harold Lockhart wrote:
>>>> David,
>>>>
>>>> When we discussed this in Luxembourg, I assumed you intended to add
>>>> an ANY to the decision request in the SAML Profile, not to the
>>>> definition of XACML policies.
>>>>
>>>> I was struck how both you and Prateek have said to me, the wire
>>>> protocol decision request is the most important part of XACML because
>>>> it allows a PDP of any kind to be called. It seems to me logically
>>>> this is the place where additional information, such as more policies
>>>> might be needed by a non-XACML PDP.
>>>>
>>>> My main concern is to make it clear that what ever is used here
>>>> should be profiled and a PDP receiving a request with contents it
>>>> does not understand MUST return Indeterminate with some appropriate
>>>> error code.
>>>>
>>>> Hal
>>>>
>>>> -----Original Message----- From: Erik Rissanen
>>>> [mailto:erik@axiomatics.com] Sent: Monday, November 23, 2009 7:12 
>>>> AM To: David Chadwick Cc: Rich Levinson; xacml Subject: [xacml] Any 
>>>> kind
>>>> of policies in a request
>>>>
>>>>
>>>> David,
>>>>
>>>> I have been thinking more about this.
>>>>
>>>> I think that an extension point to plug in any kind of policy format
>>>>  does not belong in the XACML core schema, and thus not in the
>>>> <Request>. The XACML schema is for defining the XACML language, and
>>>> we would lose some of the benefits of standardization by allowing any
>>>> content in it.
>>>>
>>>> However, SAML defined in the past a protocol for AuthZ
>>>> query/response. It is my understanding, and please correct me if I am
>>>> wrong, that there was an agreement between the SAML and XACML TCs
>>>> that the XACML request schema would supersede the SAML AuthZ formats,
>>>> and SAML dropped their own. The original SAML protocol was ambiguous
>>>> regarding the policy language.
>>>>
>>>> If we think of the XACML SAML profile to carry the legacy of the 
>>>> original SAML AuthZ protocol, than I guess it would make sense to 
>>>> support other policy languages since the original protocol was not
>>>> XACML specific.
>>>>
>>>> What do the rest of the TC see as the scope of the XACML SAML
>>>> profile? Is it just about supporting XACML, or does it have a wider
>>>> scope?
>>>>
>>>> Best regards, Erik
>>>>
>>>> David Chadwick wrote:
>>>>> Subsequent to the minutes
>>>>>
>>>>> Rich.Levinson wrote:
>>>>>
>>>>>> Proposed schema change for policies and discussion from David
>>>>>> Chadwick and response from Erik: 
>>>>>> http://lists.oasis-open.org/archives/xacml/200911/msg00023.html
>>>>>>
>>>>>> Erik: David proposed req ctx schema for ext pts xml any, where 
>>>>>> can put proprietary policy lang things; doesn't make sense to std
>>>>>> on any policies in fmt; suggest using saml/xacml mechanism Rich:
>>>>>> sees it as potentially disruptive, effectively allowing elements
>>>>>> as children of PolicySet Bill: proprietary elements don't make
>>>>>> sense; need further info to be considered;
>>>>>>
>>>>>> defer topic until more info from David addressing concerns in
>>>>>> email and minutes
>>>>>>
>>>>> It makes sense because we cannot assume that every PDP talks the
>>>>> XACML policy language. However, it is possible to make every PDP
>>>>> talk the XACML request/response context. Once we have sticky
>>>>> policies and obligations which we pass around a distributed system
>>>>> we need to be able to cater for multiple policy languages. If you
>>>>> see my presentation at W3C yesterday at
>>>>>
>>>>> http://www.w3.org/2009/policy-ws/slides/Chadwick.pdf
>>>>>
>>>>> and look at slide 5 from 11, you will see why we need to relax the
>>>>>  schema requirements on the policy element in the SAML-XACML
>>>>> profile, otherwise we have no standard way of passing a sticky
>>>>> policy to an AIPEP or Master PDP.
>>>>>
>>>>> regards
>>>>>
>>>>> David
>>>>>
>>>
>>
>
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