Re: [xacml] New Issue#66: XACML-Core 2.0,3.0 Missing attributes maybe underspecified

[Erik Rissanen <mirty@sics.se>]

Rich,

Could you clarify a couple of things about this issue? What do you see
at the intended use of the missing attribute details?

I have always thought that for interoperability, the users of XACML need
to profile XACML. They need to specify the attribute vocabulary which a
PEP must provide in the request and policy writers may refer to.

Do you intend to use the missing attribute details as a substitute for
profiling? That is, policy writers would refer to attributes, and PEP
would dynamically try to find those attributes based on the missing
attribute responses? How would the PEP find missing attributes it has
not been programmed to know about? And if it knows about the attributes,
why did it not provide the attributes in the first place?

Or is it something else you intend? (For instance submitting only a
minimum set of attributes?)

Best regards,
Erik


Rich Levinson wrote:
> I have added the following issue to the issues list:
>
>     http://wiki.oasis-open.org/xacml/IssuesList
>
> The point of the issue (below) is not to identify trivialities with
> the example, but
> to use the example as a basis for some general comments more toward
> end of the issue description. It seemed to me that using the example
> as context would be an effective way to raise the somewhat complex
> issues/concerns that are the main point here. (I will be happy to
> re-edit the issue if that makes sense after people have had a
> chance to look at it).
>
>     Thanks,
>     Rich
>
>
>         66. Missing attributes may be underspecified
>
> I did a somewhat detailed analysis of "Example two" in the core spec
> from the point of view of understanding how fine grained authorization
> (fga) (applying resource attrs to az decision) was implemented and
> came across a number of items that I think need to be addressed
> especially in potential interoperability situations. I will put all in
> one issue initially, we can decide if it needs to be broken out later.
>
> 1. line 1090-91 describing ResourceContent </xacml/ResourceContent>.
> In both the core spec and the sample messages, the ResourceContent
> </xacml/ResourceContent> contains the following:
>
>     * <ResourceContent </xacml/ResourceContent>>
>           o <md:record xmlns:md="urn:med:example:schemas:record"
>                 + xsi:schemaLocation="urn:med:example:schemas:record 
>                   http:www.med.example.com/schemas/record.xsd">
>                   <http:www.med.example.com/schemas/record.xsd%22%3E>
>                 + <md:patient>
>                       # <md:patientDoB>1992-03-21</md:patientDoB>
>                         <md:patient-number>555555</md:patient-number>
>                   </md:patient>
>             </md:record>
>       </ResourceContent </xacml/IssuesList/ResourceContent>>
>       <Attribute AttributeId
>       </xacml/AttributeId>="urn:oasis:names:tc:xacml:1.0:resource:resource-id"
>       DataType </xacml/DataType>="xs:string">
>           o <AttributeValue </xacml/AttributeValue>>
>                 + //med.example.com/records/bart-simpson.xml#
>                   xmlns(md=
>                   http:www.med.example.com/schemas/record.xsd)
>                   xpointer(/md:record/md:patient/md:patientDoB)
>             </AttributeValue </xacml/IssuesList/AttributeValue>>
>       </Attribute>
>
> While I recognize that the example itself is not intended to be
> perfect, it provides a convenient context for raising the following
> questions/issues, especially wrt fga.
>
>   1.
>
>       If this is a first request from a PEP, why is the PEP supplying
>       patient-number on line 1056? This looks like a required attr to
>       evaluate Rule 1 (line 1141), if the requestor is the patient,
>       but this example the requestor is the physician.
>
>          *
>
>             The physician-id is supplied in the request (line 1044),
>             but the only rule it appears in is rule 3 (line 1522).
>             This rule only allows "write" access (line 1507), so I
>             expect this request would probably fail as it is currently
>             set up. i.e. we would need to add a "read" action to rule
>             3 or add a physician-id test to rule 1.
>
>    *
>
>       b. Assuming the above request fails, let's consider what might
>       be done. There was a "read" request issued (line 1072), so that
>       would mean that rule 1 (line 1182), rule 2 (line 1347), or rule
>       4 (line 1668) could be applied.
>
> Rule 1 requires a Subject attribute patient-number (line 1134) to
> match the patient-number in the requested resource record (line 1141).
> Presumably a <MissingAttributeDetail </xacml/MissingAttributeDetail>>
> could be returned, somehow identifying these 2 attributes to the PEP.
>
> Rule 2 requires a patientDoB resource attr (line 1297), a
> parent-guardian-id subject attr (line 1363), and a parentGuardianId
> resource attr (line 1371). Similarly a <MissingAttributeDetail
> </xacml/MissingAttributeDetail>> could be returned requesting these.
>
>    *
>
>       Assuming this to be the case, one question I have is how does
>       the <MissingAttributesDetail </xacml/MissingAttributesDetail>>
>       tell the PEP whether the attributes that are missing should be
>       resubmitted as part of the Subject or as part of the Resource?
>       This info is provided in the Request from the xml structure,
>       however, the <MissingAttributeDetail
>       </xacml/MissingAttributeDetail>> does not have equivalent
>       structure to make such distinctions.
>
> The above is intended just to give an example of questions that occur
> for this particular example, but it is my opinion that it is
> symptomatic of a general problem of how PEPs are supposed to know how
> to construct the proper RequestContext </xacml/RequestContext>
> necessary, in general, for complex scenarios that require substantive
> fga attrs.
>
> In these more complex fga scenarios it is likely that
> <MissingAttributeDetail </xacml/MissingAttributeDetail>> will be
> typically needed to collect all the required attributes. Therefore, I
> believe some more robust mechanisms, possibly using
> MissingAttributeDetail </xacml/MissingAttributeDetail> as a good
> starting point will be needed to adequately define operation in this
> area.
>
> In this context as well, it is likely that xpaths are probably not the
> way to go since they are only applicable to certain types of resources
> (xml-based) and those resource structures are likely to change in
> time, and these changes should not percolate into the enterprise
> Policy arena. Therefore, mechanisms such as vocabularies should be
> recommended usage here with the PEP being responsible for mapping the
> vocabulary item to the particular resource physical access path such
> as the xpath.
>
> CHAMPION: Rich
>
> Status: *OPEN*
>