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Here is

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an

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example

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of

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an

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XACML

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policy

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which

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addresses

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the

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following

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requirement:

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a

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given

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resource

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can

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be

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accessed

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only

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by

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a

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user

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belonging

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to

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a

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particular

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role,

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and

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all

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requests

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to

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access

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any

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other

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resource

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should

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fail.

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Code Block
<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-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/echo/
     </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</AttributeValue>
    </Apply>
    <SubjectAttributeDesignator AttributeId="group"
     DataType="http://www.w3.org/2001/XMLSchema#string" />
   </Apply>
  </Condition>
 </Rule>
 <Rule Effect="Deny" RuleId="deny-rule" />
</Policy>

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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
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  • User - "admin" belongs only to the "admin" group
  • Result - Permit
 Code Block
<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</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/echo/</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>

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The Second XACML request
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  • User - "admin" belongs to the "admin" group and the "business" group
  • Result - Permit
 Code Block
<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</AttributeValue>
      </Attribute>
      <Attribute AttributeId="group"
       DataType="http://www.w3.org/2001/XMLSchema#string">
       <AttributeValue>business</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/echo/</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>

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The third XACML request
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  • User - "admin" belongs to the "admin" group
  • Result - Deny
 Code Block
<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</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/test/</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>

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The forth XACML request
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  • User - "admin" belongs to the "business" group
  • Result - Deny
 Code Block
<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>business</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/echo/</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>

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 Excerpt
hiddentrue
Instructions on how to write XACML policies in WSO2 Identity Server. Part 2.