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

[David Chadwick <d.w.chadwick@kent.ac.uk>]

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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David W. Chadwick, BSc PhD
Professor of Information Systems Security
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