The scenario described is exactly what we had in mind for the simple
solution. We are currently having a couple more internal
discussions, but will post the promised details on the open issues
You already touched on the main open issue, however: it actually
isn't quite clear to me to what extent the communication format for
the "callout to the ContextHandler" for missing attributes is
standardized, and if it is standardized, whether the format needs to
be changed to support our use case.
I am not sure if you got the email issues straightened out, but in
help move the thread along, I'll just include your direct email
I went over your slide presentation again, and I am trying, in
to understand the xacml part of the issue as opposed to the saml
On slide 17, you indicate a preference short term for approach 2,
I think sounds similar to the approach I would also recommend.
You characterize it as:
The way I look at situations like this, where information is need
- Policy in terms of dedicated, locally defined boolean
- PIP or PEP knows mapping to conditions over globally defined
e.g., urn:mypolicy:underage -> (urn:unitednations:birthdate
- Values of local attributes passed in request context
- Missing local attribute -> request corresponding
over global attrs
provider, is to define an attribute in the Policy that is known
in the RequestContext, and has MustBePresent set, which will force
to raise an Indeterminate condition, which can either be sent back
as MissingAttribute, or be intercepted during evaluation with a
ContextHandler as is done in the SunXacml reference
In the case at hand, I would have a condition that says:
I think the above is correct, but, in any event, what it is
to say is
For the Condition to be true:
In general, this attribute would not be found in the
a callback would
Look for an Attribute with AttributeId="urn:mypolicy:underage"
And the value of this Attribute must be true (which I assume
the user is not underage)
be initiated to try to find it. Given the name of the Issuer
(="trusted-authority") the attr finder
would know where to go with the request, which would be something
Request attribute "global:underage" for user="xxx",
So, my question is: is this along the lines that you were thinking
Approach 2, and
which would return either true or false for user "xxx",
which the attribute finder would return to the ContextHandler
which could then be compared to the required value of "true".
if so, then what more is needed, as I think this approach can be
flexible for addressing
this type of problem.
I am posting this message on behalf of Greg Neven, as he has
difficulty getting properly registered to post email to XACML
This message is relevant to the ongoing discussions from Greg's
which will continue as subject of discussion tomorrow.
-------- Original Message --------
Very sorry about the delay in answering. I thought I had subscribed to
the list, but must have done something wrong when signing up. Thanks to
David for pointing out your post to me.
Just to make sure: you are talking about the XACML request context
schema, and not SAML, right?
Embedding the predicate inside the Attribute element is indeed an
interesting option for simple predicates of the form <attribute>
<operator> <constant>, such as the birthday example that you mentioned.
It would be harder though to express more complex predicates where
operations have to be performed on the attribute itself (e.g., first 5
characters of phone number are +4144) or where multiple attributes occur
in a single predicate (e.g., graduationdate - birthdate < 18Y).
I also agree that no changes to the policy language itself would be
required, but you would have to break open the schema of the XACML
request context, right? Wouldn't that already prevent these extensions
from being defined in a profile? Because that was what I was trying to
avoid in my "simple solution". But I definitely agree that multiple
interesting issues come up in the "more challenging solution" that I
sketched: how to communicate asserted predicates to the PDP, how to
evaluate a policy against a set of asserted predicates, and also how to
determine and communicate "missing predicates".
> -------- Original Message --------
> Subject: [xacml] Attribute Assertions in XACML request
> Date: Fri, 22 Oct 2010 08:15:57 -0500
> From: Tyson, Paul H <PTyson@bellhelicopter.textron.com>
> To: xacml <firstname.lastname@example.org>
> Regarding Gregory Neven's proposal for attribute conditions in the
> request context:
> Greg's approach to put the full <Condition> element syntax in a SAML
> assertion would work. But a simple change to the <Attribute> element
> structure in the request would also work.
> <Attribute AttributeId="example:bday" DataType="date-time">
> We allow <AttributeAssertion> in place of <AttributeValue>, and move
> DataType to the parent element. We re-use the function identifiers
> already defined in XACML.
> <AttributeValue> is actually a degenerate case of attribute assertion,
> which only allows equality, or name-value pairs. <AttributeAssertion>
> generalizes this to allow other predicates besides equality.
> <AttributeAssertion FunctionId="...equals"> would be the semantic
> equivalent of <AttributeValue> for each datatype.
> In keeping with the bag-of-attribute-values paradigm for the request
> context, we would probably have to assume a bag-of-attribute-assertions
> as well. While it is OK to put the "one-and-only" restriction on
> birth-date, it might be quite reasonable to have several assertions
> about birth-date.
> (Actually this example is a bit more complicated. You probably don't
> really want to write rules about birth-date. The laws or business rules
> are about age, so your rule condition would say "age >= 18". But the
> request context might only have values or assertions about birth-dates.
> In that case the PDP needs additional information to reach a decision.
> That's another interesting topic.)
> No change to the policy language is required; however, section 7 of the
> spec would have to specify the required behavior, which might be tricky.
> A PDP implementation could, for example, use a Prolog library to test a
> rule condition, "bday < 1992-10-22" against the assertion "bday <
> 1990-10-01" to return "true". But this sort of inference depends on
> axioms and rules of deduction outside of XACML.
> I don't have Greg's email. If anyone has his email, please forward to
> To unsubscribe from this mail list, you must leave the OASIS TC that
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