Re: [xacml] Issue: Ambiguity in defn of Request wrt Attributes Category

Hi,

      

      I would say that if you are not supporting multiple decisions,
      then it's an error. It might be the case that it's not explicitly
      mentioned in the spec. We should add this to an errata item or an
      implementer guide.

      

      Best regards,

      Erik

      

      On 2013-03-04 01:00, rich levinson wrote:

    

    
      
      To TC:

      

      The "issue" here is that it does not appear to me that it
      specifies

      anywhere that a single PDP authorization decision is based on

      a set of <Attributes> element each with a different Category
      and

      that there can be at most one <Attributes> element of a
      specific

      Category involved in a single decision.

      

      I have been working under the assumption that this is true for

      quite a while now, but recently I have tried to find the
      supporting

      documentation to unambiguously validate that claim, and I have

      been unable to do so, leaving me with the conclusion that either

      the claim is wrong and that more than one <Attributes>
      element

      of the same Category can be involved in a single decision (which

      I believe to be false), or that the documentation should be
      improved

      somewhere to emphasis this fundamental point.

      

      The description in the 3.0 spec says:

      "<Attributes> [One to Many]

        Specifies information about attributes of the request context by

        listing a sequence of <Attribute> elements associated with
        an

        attribute category.

        One or more <Attributes> elements are allowed.

        Different <Attributes> elements with different categories
        are used

        to represent information about the subject, resource, action,

        environment or other categories of the access request."

      
      While the text above might lead one to believe that one might

      want to consider only including one <Attributes> element

      per Category, it says nothing definitive one way or the other.

      

      I am well aware that the multi-decision profile uses multiple

      <Attributes> elements of the same Category as the basis for

      generating a cross-product to generate "Individual Decision

      Requests", where in section 2.3.3 it states:

      "For each combination of repeated <Attributes>
        elements,

        one Individual Decision Request SHALL be created.

        This Individual Request SHALL be identical to the original

        request context with one exception:

        only one <Attributes> element

           of each repeated category

           SHALL be present."

        
      
      Again, this text is useful wrt providing the ContextHandler w the

      info it needs to generate multiple decision requests, however,

      it does not imply that this is a requirement from the PDP side.

      

      For example, what would happen if someone submitted a

      Request with two <Attributes> elements, each for a different

      Target resource, but both with the same Category, namely:

      "urn:oasis:names:tc:xacml:3.0:attribute-category:resource"?

      
      Would this be a request for which the user was asking for access

      to both resources at the same time? Or would this be an error

      if the multi-profile was not supported?

      

      I don't believe questions like this can be answered w the info in

      the specs as they currently exist. (unless, of course, I have
      missed

      something, which is entirely possible :) )

      

          Thanks,

          Rich