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Subject: RE: [xacml] Updated policy template wiki
When the original proposal for policy templates was brought forward, I noted that simply replacing a single AttributeValue element with a list of values from the policy template <Parameter> would fail in <Match>
expressions, since <Match> is very explicit about one value, one designator/selector. I offered a transform to help produce valid match expressions. AttributeDesignator does provide similar “insert-multiple-values-here” operations to the policy template substitution behavior, but I believe the suggestion of policy parameterization came up because of situations
in which AttributeDesignator cannot be used. Comparing an attribute against a static list of test values (specific to an organization or location and applied to a generic policy), for example, is a many-to-many comparison, but cannot be expressed in a <Match>
element. As we discussed on the TC call today, we’re finding more difficulties with parameter substitution the deeper we dig. Steven Legg noted in an earlier email that some Xacml functions that take single <AttributeValue>
won’t work if multiple values are dropped in to replace the <AttributeValue>. This means some sort of _expression_ transform will be necessary in condition expressions as well to move policy templates forward. In light of these increasing complexities and challenges, I’m beginning to agree with you that perhaps the policy template use case can better be addressed using the existing <AttributeDesignator>.
This would mean: 1.
Giving up parameterization behavior in <Match> expressions and moving that logic into conditions using <AttributeDesignator> to reference an attribute ID representing the parameterization data.
2.
Moving parameterization data from a static policy generator step to a PIP to fill <AttributeDesignator> references to a particular attribute ID with parameterization data in the PDP at auth request
evaluation time. Using <AttributeDesignator> instead of policy templates does impact the use case quite a bit because populating PIP data is not part of the Xacml spec. Policies could be shared between organizations per the
use case, but how the parameterization data is applied to those policies would become a vendor-specific implementation detail. I can see the attraction of parameterizing policies to allow up-front synthesis of specific policies, but as we say “the devil is in the details.” The details are winning. :/ -Danny Danny Thorpe
Authorization Architect
Dell
| Identity & Access Management, Quest Software Quest Software is not part of Dell. From: xacml@lists.oasis-open.org [mailto:xacml@lists.oasis-open.org]
On Behalf Of Erik Rissanen All,
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