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Subject: RE: [xacml] Issue#39:number of policies to return is too large

I just noted we made a mistake in defining the request context based
query which IMO makes it useless. The intention was (or at least my
intention was) to define a query which would allow the two step XACML
evaluation to be split into to parts. The PAP would do a Target match
(or partial target match) to obtain a small number of potentially
applicable policies. Then the PDP would evaluate the returned policies
to make a decision.

Unfortunately, the way the spec is written it says all the "Applicable"
policies must be returned. Looking at the core spec, this means the
policies must be fully evaluated. I don't really see any usefulness to
evaluating the policies, discarding the results and passing them over to
be evaluated again.

The spec should say that Target matched policies or potentially
applicable policies should be returned.


> -----Original Message-----
> From: Anne Anderson - Sun Microsystems [mailto:Anne.Anderson@sun.com]
> Sent: Friday, September 08, 2006 9:41 AM
> Subject: Re: [xacml] Issue#39:number of policies to return is too
> Colleagues,
> I checked with Eve Maler and Scott Cantor about this, to see what
> SAML query protocols have done.  Eve says none of the other SAML query
> protocols have tried to solve this problem; she isn't aware of anyone
> running into it either.  Scott thought the implementation-dependent
> approach I proposed was reasonable, but "in practice I'm not sure that
> this is something to be solved above SOAP.  In general, people that
> about this kind of performance issue build SAX/STAX systems to stream
> messages, not DOM. In those cases, there's no real value in breaking
> the envelope. But if you did, it seems like it should be done by
> reinventing TCP on top of SOAP (which is effectively UDP)."
> So I propose that we not try to solve this problem.  Our protocol is
> intended for use when at most a few policies will satisfy a particular
> query.  If a PAP has structured its policies such that the size of the
> response is an issue, then the PAP should not be supporting this
> protocol and should be using something else.  If the PAP does support
> the protocol, and still can't return all the applicable policies, then
> the PAP should return an error.  We should define the error in a
> standard way, however.  SAML has already defined errors that seem
> appropriate, and we can simply specify that they are to be used in
> case.
> Proposal: Add following error description to SAML profile:
> -----------
> If the PAP is unable to return all policies that apply to the request,
> the <samlp:StatusCode> Value XML attribute SHALL be
> "urn:oasis:names:tc:SAML:2.0:status:Responder" [defined in "
> SAML to mean: The request could not be performed due to an error on
> part of the SAML responder or SAML authority].  The content of the
> second-level status code SHALL be
> "urn:oasis:names:tc:SAML:2.0:status:TooManyResponses". [defined in
> to mean: "The response message would contain more elements than the
> responder is able to return."]  In this case, the response SHALL
> no Assertions.
> --------------
> Perhaps it would be acceptable to allow the PAP to return some of the
> applicable policies, but that seems like asking for trouble.
> Regards,
> Anne
> Anne Anderson - Sun Microsystems wrote On 09/06/06 10:32,:
> > Problem: What if an XACMLPolicyQuery matches more policies than the
> > is able to return in a single XACMLPolicyStatement?
> >
> > Proposal:
> >
> > Define a new optional, implementation-dependent element that MAY be
> > included in an XACMLPolicyQueryType or an XACMLPolicyStatementType.
> >
> > <element name="PolicyQueryContinuation"
> > type="xacml-saml:PolicyQueryContinuationType" />
> > <complexType name="PolicyQueryContinuationType">
> >      <xs:sequence>
> >        <xs:any namespace="##any" processContents="lax" minOccurs="0"
> >                       maxOccurs="unbounded"/>
> >      </xs:sequence>
> > </complexType>
> >
> > An instance of this element MAY be returned in an
> > "XACMLPolicyStatementType", along with Policy and/or PolicySet
> > instances.  If present, it indicates that the XACMLPolicyStatement
> > not contain all policies that match the query, and that the PDP
> > a continuation of the response.
> >
> > The request MAY then send another XACMLPolicyQuery containing the
> > instance of the PolicyQueryContinuation element to obtain more
> > that match the original query.
> >
> > The content and interpretation of the PolicyQueryContinuation
element is
> > completely implementation-dependent.  Support for it is optional.
> >
> > Regards,
> > Anne
> >
> --
> Anne H. Anderson             Email: Anne.Anderson@Sun.COM
> Sun Microsystems Laboratories
> 1 Network Drive,UBUR02-311     Tel: 781/442-0928
> Burlington, MA 01803-0902 USA  Fax: 781/442-1692

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