OPA for HTTP Authorization

Open Policy Agent[1] is a promising, light weight and very generic policy engine to govern authorization is any type of domain. I found this comparion[2] very attractive in evaluating OPA for a project I am currently working on, where they demonstrate how OPA can cater same functionality defined in RBAC, RBAC with Seperation of Duty, ABAC and XACML.  
Here are the steps to a brief demonstration of OPA used for HTTP API authorization based on the sample [3], taking it another level up.
Running OPA Server First we need to download OPA from [4], based on the operating system we are running on.  For linux, curl -L -o opa https://github.com/open-policy-agent/opa/releases/download/v0.10.3/opa_linux_amd64 Make it executable, chmod 755 ./opa Once done, we can start OPA policy engine as a server.
./opa run --server Define Data and Rules Next we need to load data and authorization rules to the server, so it can make decisions. OPA defines these in files in the format of .rego. Below is a sample …

XACML 3.0 Policies - 6

This is 6th post of a series of posts, after this post on writing XACML policies having multiple rules, http://pushpalankajaya.blogspot.com/2013/06/xacml-30-policies-multiple-rules-5.html. Here we will look into the following requirement which is more likely in practice.

  • The operation getVesrion1 and getVersion2 in the service http://localhost:8280/services/Customers should be accessed by any user
  • Request to any other service or operation should only be accessed by the users belong to the group(s) admin_emps or admin or both
Here the policy written to meet this authorization requirement,

<Policy xmlns="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17"  PolicyId="testOr" RuleCombiningAlgId="urn:oasis:names:tc:xacml:1.0:rule-combining-algorithm:first-applicable" Version="1.0">
   <Description>Test Or</Description>
   <Target></Target>
   <Rule Effect="Permit" RuleId="primary-group-emps-rule">
      <Target>
         <AnyOf>
            <AllOf>
               <Match MatchId="urn:oasis:names:tc:xacml:1.0:function:string-equal">
                  <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">read</AttributeValue>
                  <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>
               </Match>
            </AllOf>
         </AnyOf>
      </Target>
      <Condition>
         <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-at-least-one-member-of">
            <AttributeDesignator AttributeId="group" DataType="http://www.w3.org/2001/XMLSchema#string" Category="urn:oasis:names:tc:xacml:3.0:group" MustBePresent="true"></AttributeDesignator>
            <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">
               <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">admin_emps</AttributeValue>
               <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">admin</AttributeValue>
            </Apply>
         </Apply>
      </Condition>
   </Rule>
   <Rule Effect="Permit" RuleId="primary-user-rule">
      <Condition>
         <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-at-least-one-member-of">
            <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>
            <Apply FunctionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">
               <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">http://localhost:8280/services/Customers/getVersion1</AttributeValue>
               <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">http://localhost:8280/services/Customers/getVersion2</AttributeValue>
            </Apply>
         </Apply>
      </Condition>
   </Rule>
   <Rule Effect="Deny" RuleId="deny-rule"></Rule>
</Policy>

Here the first rule is to permit any requests made by users in either groups admin_emps and admin, to read any resource. Second rule will permit any request coming to operations 'http://localhost:8280/services/Customers/getVersion1(2)'. Third rule will deny any other requests.
  • User 'Pushpalanka' belonging to groups staff and business tries to access 'http://localhost:8280/services/Customers/getVersion2'. Response: Permit
<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">pushpalanka</AttributeValue>
    </Attribute>
</Attributes>
<Attributes Category="urn:oasis:names:tc:xacml:3.0:group">
    <Attribute AttributeId="group" IncludeInResult="false">
        <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">staff</AttributeValue>
        <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">business</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">http://localhost:8280/services/Customers/getVersion2</AttributeValue>
    </Attribute>
</Attributes>
</Request>
 
  • Admin user belonging to admin and business groups tries to access service 'http://localhost:8280/services/Customers/'. Response: Permit
<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">admin</AttributeValue>
    </Attribute>
</Attributes>
<Attributes Category="urn:oasis:names:tc:xacml:3.0:group">
    <Attribute AttributeId="group" IncludeInResult="false">
        <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">admin</AttributeValue>
        <AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">business</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">http://localhost:8280/services/Customers/</AttributeValue>
    </Attribute>
</Attributes>
</Request>
Cheers!

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