XACML Policy and Request

Question

first I would like to mention that this certainly a novice question, but I was looking for hours now and I do not have an answer.

I just started trying XACML for academic purposes. I use the editor provided with wso2-is to write some policies and to evaluate them against some requests.

I created this policy to express that the subject u can read or write from a resource d

     <Policy xmlns="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17" PolicyId="test-bis" RuleCombiningAlgId="urn:oasis:names:tc:xacml:3.0:rule-combining-algorithm:deny-overrides" Version="1.0">
   <Target/>
   <Rule Effect="Permit" RuleId="read-or-write">
      <Target>
         <AnyOf>
            <AllOf>
               <Match MatchId="urn:oasis:names:tc:xacml:1.0:function:string-equal">
                  <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">d</AttributeValue>
                  <AttributeDesignator AttributeId="urn:oasis:names:tc:xacml:1.0:resource:resource-id" Category="urn:oasis:names:tc:xacml:3.0:attribute-category:resource" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"/>
               </Match>
            </AllOf>
         </AnyOf>
      </Target>
      <Condition>
         <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:and">
            <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-at-least-one-member-of">
               <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">
                  <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">read</AttributeValue>
                  <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">write</AttributeValue>
               </Apply>
               <AttributeDesignator AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id" Category="urn:oasis:names:tc:xacml:3.0:attribute-category:action" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"/>
            </Apply>
            <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:any-of">
               <Function FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-equal"/>
               <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">u</AttributeValue>
               <AttributeDesignator AttributeId="urn:oasis:names:tc:xacml:1.0:subject:subject-id" Category="urn:oasis:names:tc:xacml:1.0:subject-category:access-subject" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"/>
            </Apply>
         </Apply>
      </Condition>
   </Rule>
   <Rule Effect="Deny" RuleId="deny"/>
</Policy>

While matching to this simple request "Can u read from d" I got not applicable as result ! Here is the request:

 <Request xmlns="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17" CombinedDecision="false" ReturnPolicyIdList="false">
<Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-category:action">
<Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">read</AttributeValue>
</Attribute>
</Attributes>
<Attributes Category="urn:oasis:names:tc:xacml:1.0:subject-category:access-subject">
<Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:subject:subject-id" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">u</AttributeValue>
</Attribute>
</Attributes>
<Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-category:resource">
<Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:resource:resource-id" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">d</AttributeValue>
</Attribute>
</Attributes>
</Request> 

Anyone can help me on understanding what I'm doing wrong?

Thank you all!

Answer 1

I tested the policy and the request you sent in the Axiomatics Policy Server (disclaimer: I work for Axiomatics). The answer should in fact be Deny. Both rules triggered. You combined the rules inside a policy with a deny-overrides combining algorithm which means that Deny wins over Permit.

You can see below a screenshot of the policy simulation in APS which shows both rules being triggered and the second rule winning over the first one.

If you are interested in understanding combining algorithms better, here's the "truth table" for deny-overrides:

Answer 2

As you are getting "Not Applicable" it seems that your policy is either not enabled in WSO2 IS or not promoted to PDP for testing. Just check if the policy is enabled and promoted to PDP for test. You may also test the policy without promoting to PDP but in both the cases it should be in enabled mode.

I tried your policy in WSo2 IS 4.0.0 and its giving "Deny". And yes as David mentioned its because your policy combining algorithm is "deny-overrides" which is always getting "Deny" as per your default rule as below:

<Rule Effect="Deny" RuleId="deny"/>

So either you need to make your policy combining algorithm as "permit-overrides" or drop the last rule.

Answer 3

Yuor Request is fine and here's the Policy for your Reqirement.

<Policy xmlns="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17" PolicyId="9f654de2-06d3-45c9-bb7f-947c9a9b247a" RuleCombiningAlgId="urn:oasis:names:tc:xacml:1.0:rule-combining-algorithm:first-applicable" Version="1.0">
<Target>
<AnyOf>
<AllOf>
<Match MatchId="urn:oasis:names:tc:xacml:1.0:function:string-equal">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">d</AttributeValue>
<AttributeDesignator AttributeId="urn:oasis:names:tc:xacml:1.0:resource:root-resource-id" Category="urn:oasis:names:tc:xacml:3.0:attribute-category:resource" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"/>
</Match>
</AllOf>
</AnyOf>
</Target>
<Rule Effect="Permit" RuleId="Rule_write">
<Condition>
<Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:and">
<Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-at-least-one-member-of">
<Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">write</AttributeValue>
</Apply>
<AttributeDesignator AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id" Category="urn:oasis:names:tc:xacml:3.0:attribute-category:action" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"/>
</Apply>
<Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-at-least-one-member-of">
<Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">u</AttributeValue>
</Apply>
<AttributeDesignator AttributeId="urn:oasis:names:tc:xacml:1.0:subject:subject-id" Category="urn:oasis:names:tc:xacml:1.0:subject-category:access-subject" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"/>
</Apply>
</Apply>
</Condition>
</Rule>
<Rule Effect="Permit" RuleId="Rule_read">
<Condition>
<Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:and">
<Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-at-least-one-member-of">
<Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">read</AttributeValue></Apply>
<AttributeDesignator AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id" Category="urn:oasis:names:tc:xacml:3.0:attribute-category:action" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"/>
</Apply><Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-at-least-one-member-of">
<Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">u</AttributeValue></Apply>
<AttributeDesignator AttributeId="urn:oasis:names:tc:xacml:1.0:subject:subject-id" Category="urn:oasis:names:tc:xacml:1.0:subject-category:access-subject" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"/>
</Apply>
</Apply>
</Condition>
</Rule>
<Rule Effect="Deny" RuleId="Rule_Deny_All"/>
</Policy>