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WSO2 Identity Server (WSO2 IS) can be used to create and enforce policies in an authorization flow to ensure fine-grained authorization.

Let's take a look at a sample scenario to understand how WSO2 IS supports fine-grained authorization using XACML requests and responses in JSON format via REST calls.

Consider a sample scenario where a user requests authorization to a resource registered in WSO2 IS. When WSO2 IS recieves the request, an enforced policy will be evaluated and the Policy Decision Point (PDP) in WSO2 Identity Server decides whether or not to grant the user access to the resource. 

The following topics walk you through the steps you need to follow to try out the sample scenario: 

Prerequisites

Procedure

Follow the steps below to publish a sample policy to the PDP in WSO2 Identity Server:

  1. Access the WSO2 IS Management Console via https://localhost:9443/carbon/, and sign in using admin/admin as credentials.
  2. Click the Main tab on the Management Console, go to Entitlement -> PAP and then click Policy Administration. The Policy Administration screen appears.
  3. Click Add New Entitlement Policy. This displays the available policy creation methods.
  4. Click Write Policy in XML. This allows you to write a XACML policy based on your requirement using the XML editor.
  5. Add the following sample policy and click Save Policy:

    <Policy xmlns="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17"  PolicyId="web-filter-policy-1" 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">index.jsp</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"></AttributeDesignator>
                </Match>
             </AllOf>
          </AnyOf>
       </Target>
       <Rule Effect="Permit" RuleId="Rule_for_all_groups">
          <Target>
             <AnyOf>
                <AllOf>
                   <Match MatchId="urn:oasis:names:tc:xacml:1.0:function:string-equal">
                      <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">publicUser</AttributeValue>
                      <AttributeDesignator AttributeId="http://wso2.org/identity/user/username" Category="http://wso2.org/identity/user" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"></AttributeDesignator>
                   </Match>
                </AllOf>
             </AnyOf>
          </Target>
          <Condition>
             <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">view-welcome</AttributeValue>
                   <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">view-summary</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"></AttributeDesignator>
             </Apply>
          </Condition>
       </Rule>
       <Rule Effect="Permit" RuleId="Rule_for_all_internal_user_group">
          <Target>
             <AnyOf>
                <AllOf>
                   <Match MatchId="urn:oasis:names:tc:xacml:1.0:function:string-equal">
                      <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">internalUser</AttributeValue>
                      <AttributeDesignator AttributeId="http://wso2.org/identity/user/username" Category="http://wso2.org/identity/user" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"></AttributeDesignator>
                   </Match>
                </AllOf>
             </AnyOf>
          </Target>
          <Condition>
             <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">view-status</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"></AttributeDesignator>
             </Apply>
          </Condition>
       </Rule>
       <Rule Effect="Permit" RuleId="Rule_for_all_admin_user_group">
          <Target>
             <AnyOf>
                <AllOf>
                   <Match MatchId="urn:oasis:names:tc:xacml:1.0:function:string-equal">
                      <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">adminUser</AttributeValue>
                      <AttributeDesignator AttributeId="http://wso2.org/identity/user/username" Category="http://wso2.org/identity/user" DataType="http://www.w3.org/2001/XMLSchema#string" MustBePresent="true"></AttributeDesignator>
                   </Match>
                </AllOf>
             </AnyOf>
          </Target>
          <Condition>
             <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">modify-welcome</AttributeValue>
                   <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">modify-summary</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"></AttributeDesignator>
             </Apply>
          </Condition>
       </Rule>
       <Rule Effect="Deny" RuleId="Rule_deny_all"></Rule>
       <ObligationExpressions>
          <ObligationExpression FulfillOn="Deny" ObligationId="fail_to_permit">
             <AttributeAssignmentExpression AttributeId="obligation-id">
                <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">You can not access the resource index.jsp</AttributeValue>
             </AttributeAssignmentExpression>
          </ObligationExpression>
       </ObligationExpressions>
    </Policy>

    This adds the sample policy to the Available Entitlement Policies list.

  6. Click Publish to My PDP applicable to the sample policy that you added. This takes you to the Publish Policy screen.
  7. Click Publish. This displays a confirmation message asking whether you want to continue publishing to PDP.
  8. Click Yes. This publishes the policy to the PDP.

Now that you have published the policy, you can send a sample request to see how the policy evaluates the request.

Testing the authorization flow

You can use any REST client to send a sample request. In this tutorial we are going to use the Google Chrome Postman app.


First, send a sample request that the policy can evaluate and provides a response with the decision as deny. 

Ensure that you specify the following when you send the sample request using the REST client:

  • Request type should be POST.
  • Endpoint URL should be https://<wso2-is-host>:<port>/api/identity/entitlement/decision/pdp.
  • Authorization should be basic base64Encoded username and password.
  • Content type should be application/json.


You can send the following as the first sample request:

{
   "Request": {
      "http://wso2.org/identity/user": {
         "Attribute": [
            {
               "AttributeId": "http://wso2.org/identity/user/username",
               "Value": "adminUser",
               "DataType": "string",
               "IncludeInResult": true
            }
         ]
      },
     
      "Resource": {
         "Attribute": [
            {
               "AttributeId": "resource-id",
               "Value": "index.jsp",
               "DataType": "string",
               "IncludeInResult": true
            }
         ]
      },
      "Action": {
            "Attribute": [{
                    "AttributeId": "action-id",
                    "Value": "view-welcome",
                    "DataType": "string",
                    "IncludeInResult": true
                }
            ]
        }
        
   }
}

Here, http://wso2.org/identity/user is a custom XACML category in WSO2 Identity Server. This category has http://wso2.org/identity/user/username as a custom attribute Id.

In the above request since the IncludeInResult property of each attribute is set to true, each attribute will be included in the the response. If you do not want each attribute to be included in the response you can set the IncludeInResult property of each attribute to false. Then the response will be short.

Next, send a sample request that the policy can evaluate and provides a response with the decision as Deny

You can send the following as the sample request:

{
   "Request": {
      "http://wso2.org/identity/user": {
         "Attribute": [
            {
               "AttributeId": "http://wso2.org/identity/user/username",
               "Value": "adminUser",
               "DataType": "string",
               "IncludeInResult": false
            }
         ]
      },
     
      "Resource": {
         "Attribute": [
            {
               "AttributeId": "resource-id",
               "Value": "index.jsp",
               "DataType": "string",
               "IncludeInResult": false
            }
         ]
      },
      "Action": {
            "Attribute": [{
                    "AttributeId": "action-id",
                    "Value": "modify-welcome",
                    "DataType": "string",
                    "IncludeInResult": false
                }
            ]
        }
        
   }
}


Analyzing the response

You will see the following response whe you send the first sample request given above:

{
    "Response": [
        {
            "Decision": "Deny",
            "Status": {
                "StatusCode": {
                    "Value": "urn:oasis:names:tc:xacml:1.0:status:ok"
                }
            },
            "Obligations": [
                {
                    "Id": "fail_to_permit",
                    "AttributeAssignments": [
                        {
                            "AttributeId": "obligation-id",
                            "Value": "You can access the resource index.jsp",
                            "DataType": "http://www.w3.org/2001/XMLSchema#string"
                        }
                    ]
                }
            ],
            "Action": {
                "Attribute": [
                    {
                        "AttributeId": "urn:oasis:names:tc:xacml:1.0:action:action-id",
                        "Value": "view-welcome",
                        "IncludeInResult": "true",
                        "DataType": "http://www.w3.org/2001/XMLSchema#string"
                    }
                ]
            },
            "http://wso2.org/identity/user": {
                "Attribute": [
                    {
                        "AttributeId": "http://wso2.org/identity/user/username",
                        "Value": "adminUser",
                        "IncludeInResult": "true",
                        "DataType": "http://www.w3.org/2001/XMLSchema#string"
                    }
                ]
            },
            "Resource": {
                "Attribute": [
                    {
                        "AttributeId": "urn:oasis:names:tc:xacml:1.0:resource:resource-id",
                        "Value": "index.jsp",
                        "IncludeInResult": "true",
                        "DataType": "http://www.w3.org/2001/XMLSchema#string"
                    }
                ]
            }
        }
    ]
}

The response that you get when you set the IncludeInResult property of each attribute to false in the request is as follows:

{
    "Response": [
        {
            "Decision": "Deny",
            "Status": {
                "StatusCode": {
                    "Value": "urn:oasis:names:tc:xacml:1.0:status:ok"
                }
            },
            "Obligations": [
                {
                    "Id": "fail_to_permit",
                    "AttributeAssignments": [
                        {
                            "AttributeId": "obligation-id",
                            "Value": "You can not access the resource index.jsp",
                            "DataType": "http://www.w3.org/2001/XMLSchema#string"
                        }
                    ]
                }
            ]
        }
    ]
}

You will see that the response is comparatively short.

You will see the following response when you send the second sample request given above.

{
    "Response": [
        {
            "Decision": "Permit",
            "Status": {
                "StatusCode": {
                    "Value": "urn:oasis:names:tc:xacml:1.0:status:ok"
                }
            }
        }
    ]
}

You see this response with the decision as Permit for the second sample request because the sample policy specifies to print the obligation only if the decision is Deny.

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