Creating a XACML Policy

At the root of all XACML policies is a Policy or a PolicySet. A Policy represents a single access control policy, expressed through a set of rules. A PolicySet is a container that can hold other Policies or PolicySets, as well as references to policies found in remote locations. Each XACML policy document contains exactly one Policy or PolicySet root XML tag. Because a Policy or PolicySet may contain multiple policies or Rules, each of which may evaluate to different access control decisions, XACML needs some way of reconciling the decisions each makes. This is done through a collection of Combining Algorithms. Each algorithm represents a different way of combining multiple decisions into a single decision.

WSO2 Identity Server XACML support will provide two methods of writing an XACML Policy.

• Some predefined commonly used XACML Policy template samples where you can use by editing according to your use case.
  

  Note

   To get more details on available XACML templates. Read me.

• A set of UI editors to create an XACML policy using UI configurations.

Here, in this documentation, we will mainly focus on how to create an XACML policy using UI of our management console of WSO2 IS. Please follow the below steps in management console,

1. Sign in. Enter your username and password to log on to the Management Console.
2. Navigate to the Main menu to access the Entitlement menu. Click Policy Administration under PAP.
3. Click Add New Entitlement Policy.
   

The Add New Policy page appears which gives the 6 ways of writing an XACML 3.0 policy. You can select one out of six methods to create the policy using UI according to your preference as follows.

Simple Policy Editor

• This simple editor provides you the opportunity to create XACML 3.0 policies without any knowledge of XACML policy language. You can define your rules in a simpler manner and create an XACML 3.0 policy out of them. However, you need to have some knowledge about access control rules.
  
  

This editor is based on four categories which we are mostly talking about access control rules. i.e User, Resource, Action, and Environment where  User is the person who is going to access the resource,  Resource is an entity that we are trying to protect with access control rules,  Action is, what user is going to perform on Resource and Environment is the time, domain or any other factors that could cause to control the user’s access.

A sample policy example: This policy is defined for accessing “foo” resource

Following are the access control rules that policy needs to be satisfied

• Rule1: Resources under “foo” collection can be read, written, edited and deleted by the users in the admin role.
• Rule 2: Resources under “foo/wso2″ collection can be read by only the users in the WSO2 (whose email address is wso2.com domain) regex for email (^([a-zA-Z0-9_.-])+@wso2.com)between 9.00am and 4.00pm (09:00:00+05:00, 16:00:00+05:00)
• All other access request to “foo” resource must be denied.

You can build the above-mentioned policy example using Simple Policy Editor as shown below. Here, "foo" can be the main resource and the other resource “foo/wso2″ can be the child resource. If you have further resources to evaluate you can add them as child resources by clicking on the icon and create separate rules.

Basic Policy Editor

• This editor is based on four categories which we are mostly talking about access control rules. i.e Subject, Resource, Action and Environment.
• You can define a target and multiple rules in the policy. Rules can be ordered.
• You can plug any attribute value sources and select those attribute values when creating the policy; rather than filling text boxes by your own. By default, WSO2 registry resources, Roles of the underline user store and some pre-defined actions are the attribute value sources for the resource, subject and action attributes respectively. There are extension points that you can use to extend and bring more attribute values on to the policy editor UI.

A sample policy requirement: 

• This access control policy is written for the patient records of Medi Hospital. Patient records are stored in a location under “/patient/” directory. Therefore we are defining access control rules for “/patient/” directory.
• Users can only access patient records from 09.00pm to 04.00pm.
• Patient records can be created, deleted by users in MedAdminstrator role.
• Patient records can be updated and read by users in MediStaff role.
• All other access requests to patient records must be denied.

Let's implement this sample policy using Basic Policy Editor,

Step1: Define a name for the policy.

Step 2:  This is similar as defining the policy target element. Configure it such as  “policy is applied for resource attribute value /patient//*  with reg-ex match”.

Step 3: Define the 1st rule. The rule is “Users can only access patient records from 09.00pm to 04.00pm”. It means that if the user tries to access records any other time, the user must be denied. Therefore, we are writing a deny rule for users who are not accessing patient records from 09.00pm to 04.00pm. Therefore first, let's define a rule name and also define the rule effect as “Deny”. Then Select “Time” from the environment. Select functions as “is not” and “greater than and less than”. Write the time with GMT offset value. After defining you can add this rule into the policy.

Step 4: Define the 2nd rule. Rule name must be given. Then select “Role” as user’s attribute. You can select your “MedAdminstrator” role name from user attribute source. So just click on the icon.

Step 5: You can do a search for attributes values.

Step 6: Select only the “MediAdminstrator” role from the attribute source.

Step 7: You can see a text box has been filled with the selected “MediAdminstrator” role name. Now let define actions. Here let us make the function name as “at-least-one”. Then this rule would be satisfied even when at least one action is going to perform.  Finally, let us add this rule into the policy. 

Step 8:  Let's define the 3rd rule.  Which allows “MediStaff” roles to access the resource with action read and edit.  You can follow same steps 4, 5, 6, 7.   Then finally, add this rule in to the policy.

Step 9: Finally define the rule to deny all other access,  as following

Step 10:  We have defined the target and rules.  Now it is time to define the rule-combining algorithm.  Let select is as  “first applicable” Then rule effect of the 1st  rule that is evaluated properly,  would be the final result of the policy.  

 You can click on “finish” and finish policy creation.

Standard Policy Editor

• The standard policy editor is little similar to Basic Policy Editor. But it is basically designed for creating XACML 3.0 policy rules. Because there are several improvements with Obligation in XACML 3.0 when compare to 2.0. In XACML 2.0, obligations can only be added to policies and policy sets. But with XACML 3.0, rules can also contain Obligations. Therefore, if you want to get details of the obligations after the policy evaluated, It is good to use Standard Policy Editor. 
• As in Basic Policy Editor, there is a place to define the conditions which make the rules evaluated as "The policy is evaluated only when following are matched" and a place to define entitlement rules.
• Advice is a newly introduced feature with XACML 3.0 which is similar to Obligations. But only different, when compared to Obligations, PEPs do not have to comply with advice statements. PEPs can consider or discard the statement. Common use case is to explain why something was denied. “User bob is denied Because he has not a valid email”
• Here the attribute "Define Policy Obligation or Advice" is not mandatory.

A sample policy requirement: 

• This access control policy is written for the patient records of Medi Hospital. Patient records are stored in a location under “/patient/” directory. Therefore we are defining access control rules for “/patient/” directory.
• Users can only access patient records from 09.00pm to 04.00pm.
• Patient records can be created, deleted by users in MedAdminstrator role.
• Patient records can be updated and read by users in MediStaff role.
• All other access requests to patient records must be denied.

Since this editor is very similar to Basic Policy Editor we can use the same steps from Step 1 to Step 9 to configure the above requirement in Advance Policy Editor.

Step 10: In advance, if we want to see the details of the obligation after the policy evaluated, you can

You can define a policy obligation or advice as follows:

Step 11:  We have defined the target, rules, and obligation.  Now it is time to define the rule-combining algorithm.  Let select is as  “first applicable” Then rule effect of the 1st  rule that is evaluated properly,  would be the final result of the policy.  

 You can click on “finish” and finish policy creation.

Policy Set Editor

When you want to create a set of policies to evaluate at one time, you can create a Policy Set. You can add policies as shown in the figure and Click "Finish" to create the policy set.

Import Existing Policy

You can add a policy by using a policy XML file. 

• Write a policy in an XML file and upload it.

Write Policy in XML

Click Finish/Upload depending on the option you chose to create your policy.