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.
- We provide some Some predefined commonly used XACML Policy template samples where you can use by editing according to your use case. To
templates please readInfo title Note To get more details on available
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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,
- Navigate to the Main menu to access the Entitlement menu. Click Policy Administration under PAP.
- Click Add New Entitlement Policy.
The Add New Policy page appears . The WSO2 Identity Server has 6 which gives the 6 ways of writing a an XACML 3.0 policy. You can select one out of six methods to create the policy using UI accoring to your preference as follows.
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- 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 where User is the person who is going to access the resource, Resource is entity that we are trying to protect with access control rules, User is the person who is going to access the resource, 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.
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Entitlement Policy Name: Name of the policy. Entitlement Policy Description: A description of the policy. This policy is based on: Define based on what entity, that you are going to write this policy.
You can define multiple permit rules: As an example, “Only users in admin role can do GET” This rule can be defined as follows. You need to select “Role” attribute id for “User” and fill the text box with the role name (admin) and then fill the text box of near “Action” with action name (GET) Deny rule is automatically created as the final rule. Permitted rules are evaluated from top to blow.
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A sample policy example:
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This policy is defined for accessing “foo” resource
following 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.
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Entitlement Policy Name: Name of the policy. Entitlement Policy Description: A description of the policy. The policy is going to be evaluated Only when following matched: You can define; for what attribute values, this policy is going to be applied (or picked). This is similar to defining the policy target element. Define Entitlement Rule(s): You can define rules which you want to evaluate after they are matched with above. |
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 request to patient records must be denied.
Lets implement this sample policy using Basic Policy Editor,
Step1: Define a name for the policy.
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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, user must 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 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.
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- 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.
You can define a policy obligation or advice as follows:
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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 request 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 10: We have defined the target and four 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.
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There are Policy Combining Algorithms which are used by Policy Sets and Rule Combining Algorithms which are used by Policies. Each of the algorithms mentioned below has its Policy Combining algorithm and its Rule Combining algorithms as follows:
These algorithms are explained in detail as follows,
This combining algorithm combines decisions in such a way that if any decision is a Permit, then that decision wins. The permit overrides combining algorithm can be interesting when: At least one child must return a Permit for access to be granted overall regardless of restrictions. One wants to return all the reasons why access is being denied. This is what one could call a “greedy deny overrides”.Forinstanceifthe reason for not being able to view a resource is that(a) you are not the owner and (b) you are in the wrong department, then we could rework the previous example as follows. When any of the deny reason triggers, the response wouldbe denywith all the applicable reasons for access being denied:
This combining algorithm exists only for policy sets to combine policy sets and policies. It cannot be used to combine rules. With this combining algorithm, in order for either of a Permit or Deny to be returned, then only one of the children must produce a valid decision – whether Deny or Permit.
The ordered combining algorithms combine decisions in the same way as their (unordered) cousins. In, addition they bring the guarantee that policies, policy sets, and rules are considered in the order in which they are defined. The need to define an ordered combining algorithm stems from the fact the XACML specification does not specify whether order matters in the deny-overrides and permit-overrides combining algorithms. |
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.
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