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Writing XACML policies in WSO2 Identity Server - 3

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Last updated: Jul 12, 2012Version comment
6 min read

This article addresses the following authorization requirements.

1. The operation getCustomers in the service "http://localhost:8280/services/Customers" should only be accessed by users belonging to the admin_customers group.
2. The operation getEmployees in the service "http://localhost:8280/services/Customers" should only be accessed by users belonging to the admin_emps group.
3. Requests to any other service or operation should fail.

<?xml version="1.0" encoding="UTF-8"?>
    <Policy PolicyId="urn:sample:xacml:2.0:samplepolicy"
      RuleCombiningAlgId="urn:oasis:names:tc:xacml:1.0:rule-combining-algorithm:first-applicable" xmlns="urn:oasis:names:tc:xacml:2.0:policy:schema:os">
      <Description>Sample XACML Authorization Policy</Description>
      <Target>
        <Subjects>
          <AnySubject/>
        </Subjects>
        <Actions>
          <AnyAction/>
        </Actions>
        <Resources>
          <AnyResource/>
        </Resources>
      </Target>
      <Rule Effect="Permit" RuleId="primary-group-customer-rule">
        <Target>
          <Subjects>
            <AnySubject/>
          </Subjects>
          <Resources>
            <Resource>
              <ResourceMatch MatchId="urn:oasis:names:tc:xacml:1.0:function:string-regexp-match">
                <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">http://localhost:8280/services/Customers/getCustomers</AttributeValue>
                <ResourceAttributeDesignator
                  AttributeId="urn:oasis:names:tc:xacml:1.0:resource:resource-id" DataType="http://www.w3.org/2001/XMLSchema#string"/>
              </ResourceMatch>
            </Resource>
          </Resources>
          <Actions>
            <Action>
              <ActionMatch MatchId="urn:oasis:names:tc:xacml:1.0:function:string-equal">
                <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">read</AttributeValue>
                <ActionAttributeDesignator
                  AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id" DataType="http://www.w3.org/2001/XMLSchema#string"/>
              </ActionMatch>
            </Action>
          </Actions>
        </Target>
        <Condition>
          <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-subset">
            <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">
              <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">admin_customers</AttributeValue>
            </Apply>
            <SubjectAttributeDesignator AttributeId="group" DataType="http://www.w3.org/2001/XMLSchema#string"/>
          </Apply>
        </Condition>
      </Rule>
      <Rule Effect="Permit" RuleId="primary-group-emps-rule">
        <Target>
          <Subjects>
            <AnySubject/>
          </Subjects>
          <Resources>
            <Resource>
              <ResourceMatch MatchId="urn:oasis:names:tc:xacml:1.0:function:string-regexp-match">
                <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">http://localhost:8280/services/Customers/getEmployees</AttributeValue>
                <ResourceAttributeDesignator
                  AttributeId="urn:oasis:names:tc:xacml:1.0:resource:resource-id" DataType="http://www.w3.org/2001/XMLSchema#string"/>
              </ResourceMatch>
            </Resource>
          </Resources>
          <Actions>
            <Action>
              <ActionMatch MatchId="urn:oasis:names:tc:xacml:1.0:function:string-equal">
                <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">read</AttributeValue>
                <ActionAttributeDesignator
                  AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id" DataType="http://www.w3.org/2001/XMLSchema#string"/>
              </ActionMatch>
            </Action>
          </Actions>
        </Target>
        <Condition>
          <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-subset">
            <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">
              <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">admin_emps</AttributeValue>
            </Apply>
            <SubjectAttributeDesignator AttributeId="group" DataType="http://www.w3.org/2001/XMLSchema#string"/>
          </Apply>
        </Condition>
      </Rule>
      <Rule Effect="Deny" RuleId="deny-rule"/>
    </Policy>

The following are a few valid requests which will result in "Permit/Not Applicable/Deny" once evaluated against the above policy.

The first XACML request

  • Resource - http://localhost:8280/services/Customers/getCustomers
  • User - "admin" belongs only to the "admin_customers" group
  • Result - Permit
<Request xmlns="urn:oasis:names:tc:xacml:2.0:context:schema:os"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
     <Subject>
      <Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:subject:subject-id"
       DataType="http://www.w3.org/2001/XMLSchema#string">
       <AttributeValue>admin</AttributeValue>
      </Attribute>
      <Attribute AttributeId="group"
       DataType="http://www.w3.org/2001/XMLSchema#string">
       <AttributeValue>admin_customers</AttributeValue>
      </Attribute>
     </Subject>
     <Resource>
      <Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:resource:resource-id"
       DataType="http://www.w3.org/2001/XMLSchema#string">
       <AttributeValue>http://localhost:8280/services/Customers/getCustomers</AttributeValue>
      </Attribute>
     </Resource>
     <Action>
      <Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id"
       DataType="http://www.w3.org/2001/XMLSchema#string">
       <AttributeValue>read</AttributeValue>
      </Attribute>
     </Action>
     <Environment />
    </Request>

The second XACML request

  • Resource - http://localhost:8280/services/Customers/getCustomers
  • User - "admin" belongs only to the "admin_emps" group
  • Result - Deny
<Request xmlns="urn:oasis:names:tc:xacml:2.0:context:schema:os"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
     <Subject>
      <Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:subject:subject-id"
       DataType="http://www.w3.org/2001/XMLSchema#string">
       <AttributeValue>admin</AttributeValue>
      </Attribute>
      <Attribute AttributeId="group"
       DataType="http://www.w3.org/2001/XMLSchema#string">
       <AttributeValue>admin_emps</AttributeValue>
      </Attribute>
     </Subject>
     <Resource>
      <Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:resource:resource-id"
       DataType="http://www.w3.org/2001/XMLSchema#string">
       <AttributeValue>http://localhost:8280/services/Customers/getCustomers</AttributeValue>
      </Attribute>
     </Resource>
     <Action>
      <Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id"
       DataType="http://www.w3.org/2001/XMLSchema#string">
       <AttributeValue>read</AttributeValue>
      </Attribute>
     </Action>
     <Environment />
    </Request>