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Subject: Re: [xacml] Preliminary review of WS-XACML
Rich, I still dont understand why there is an interesting use-case for combining WS-Policy and XACML. Why would an entity advertise its authorization policies using WS-Policy? An example would probably help folks like me who have a superficial understanding of XACML. - prateek > At the last XACML TC mtg, Jun 5, I agreed to raise my concerns > about WS-XACML to the TC list about pushing XACML policy > expressions to the periphery in the sense that they would appear > within WS-Policy assertions. > > In the process, I have reviewed the spec again and have a number > of detailed comments to make about it, but have not yet had the > time to assemble everything together in a cohesive fashion, so in > the interest of keeping things moving, I will provide a summary of > my findings here. > > As a result of this recent review, I have revised my thinking > considerably > about this spec. In particular, I believe in my early reviews of the > material > I had underestimated the scope of what the spec is trying either > explicitly > or implicitly to accomplish. At one level, I can now see it as a serious > attempt at a "grand unification theory" of XACML and WS-Policy. > > The first major factor that the spec addresses is an abstraction of > WS-Policy, > itself. In particular, by representing assertions as combinations of > Requirements > and Capabilities, the spec makes explicit the structure of WS-Policy > which is > somewhat lost in the extremely abbreviated assertion representations > found > in specs such as WS-SecurityPolicy. (Note: there are background refs, > which > include a representation of WS-SP using the same constructs used in > WS-XACML, > which I have not reviewed yet, but does promise to be interesting.) > > The 2nd major factor the spec addresses is the notion of vocabularies, > where > a vocabulary is associated with a policy domain, such as authorization, > privacy, or system-specific policy domains. In each vocabulary is a > mechanism > for expressing constraints on the variables within the vocabulary. The > constraints, > themselves, are abstracted so that basically any policy domain can be > mapped > into a XACML policy domain, and theoretically the client and server can > determine dynamically whether their respective Requirements and > Capabilities > are mutually acceptable. Generally, the client does the evaluation of > its own > assertions vs the assertions it obtains from the server's wsdl. > > A 3rd major factor that is only lightly touched on is the notion that > the "advertised" > or "published" policy (i.e. that which appears as assertions in > WS-Policy) MUST > be a subset of the "internal" or enterprise policy used by the policy > publisher > for policy evaluation. There is a brief section (10) that talks about > "managing" > policies and how segments of internal policy might be tagged for > external publication. > > A 4th significant factor is the list of supported constraint functions > in Appendix A. > These are clearly a subset of the more general xacml function set. > Some information > needs to be elaborated as to where the lines are drawn between > core-xacml and > ws-xacml functions and any significance there is to that boundary. > > It becomes quickly apparent that when we model the whole situation we > have > possibly 4 or 5 familiar actors involved in the overall process: > > - the service, itself, with its advertised wsdl > - the client, with its own internal capabilities represented as > assertions > - the PEP, that intercepts the client request and is responsible > for constructing > a XACML authorization request based on the request and other > available > context. > - the PDP, that processes the authorization request against its set > of policies. > - an admin entity that specifies the policy that is used by the PDP > and the > advertised policy that is published by the service. > > This is a broader model than that which is envisioned in the original > xacml core > spec, particularly the domain of advertised policy which until now has > been > pretty much the exclusive domain of WS-Policy. > > My basic conclusion is that the spec appears to be quite sound in > concept and > detail. However, the breadth of its scope is such that a significant > amount of > additional analysis is needed to determine if the abstractions are > optimal for the > overall problem space being addressed or whether they carry the inherent > complexity and capabilities of xacml out to a space where a less complex > expression mechanism would be more appropriate. > > It seems appropriate to me that the TC might want to spend some cycles > addressing the high level problem space that WS-XACML is addressing > and determine if we think this spec is worth promoting for the broad > purposes that it appears capable of addressing. > > Thanks, > Rich > > --------------------------------------------------------------------- > To unsubscribe from this mail list, you must leave the OASIS TC that > generates this mail. You may a link to this group and all your TCs in > OASIS > at: > https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php
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