Introduction to XACML Fine Grained Authorization
When we talk about a resource (Here, a resource is the Web App hosted in WSO2 Application Server, Apache Tomcat etc.), we have to talk about the authority granted to users who access that resource. That means, some users are authorized to use the Web App while some users are not. So what does Fine Grained Authorization mean? Traditionally, the authority granted to the user of the resource depends on the user, the resource and the action which the user does on the resource. However, if we can provide authority based on the user, the resource, actions the user does on the resource, environment, time, user's role etc, the authority we grant can be described as fine grained authority. That is, we use more details from the user scenario in order to determine the authority that should be granted to the user.
Example of a fine grained authority requirement: " This document can be edited only by PersonX, who is a Teacher and between 8am to 10am in the school office premises".
To evaluate such a requirement against a user request, we have to document those fine grained details of the requirement. These documents are called Polices and XACML is used to document this type of policies. We can evaluate a user's requirements against these XACML policies using an XACML engine. WSO2 Identity Server can be used for this purpose. WSO2 IS has an XACML Policy Engine where users can evaluate their requests and it provides many functionalities related to XACML Authorization.
Providing XACML Fine Grained Authorization to WebApp Requests
WSO2 Application Server, Apache Tomcat or any other web container can be used to host our web apps. If it is required to provide fine grained access (authority) to our Web Apps, WSO2 Identity Server can be used as the XACML Policy Decision Point (PDP). This PDP can be accessed via a web service called Entitlement Service. We use the servlet filter named Entitlement Servlet Filter as the Policy Enforcement Point (PEP) for Web App authorization. This allows us the flexibility of using it in any Web App container. The Entitlement Servlet Filter uses a proxy to communicate with WSO2 Identity Server.
The following digram shows how the servlet filter receives the decision on user authority:
To get an entitlement decision, we need some parameters like UserName, ResourceName, Action and Environment. We can map the resource name to the servlet to which the request is sent. Environment will be the WebApp. Action will be the HTTP action GET, POST etc. In order to get the user name of the person who sent the Web App request, the following Java EE authentication mechanisms are used:
• Basic Authentication
• Client Cert Authentication
• Digest Authentication
• Form Authentication
To grant authority, we have to authenticate the person. After the authentication, we can obtain the username in the servlet filter using the above mentioned methods. All the parameters can be obtained to get an entitlement decision. As shown in the diagram, when a request comes to a particular Web App which has the engaged Entitlement Servlet Filter, the following parameters are obtained: UserName, ResourceName, Action and Environment. Then the PDP Proxy is initialized to communicate with WSO2 IS. After that, the parameters are sent as an XACML request and the entitlement decision is received. Depending on the entitlement decision received, the request which has came to the Web App is either stopped or passed.
The next critical step in this process is for the user to engage the Entitlement Servlet Filter. For that, we use the web.xml. From this file, the servlet filter will read necessary parameters in order to initialize the communication with WSO2 IS. The following shows an example web.xml which configures the Entitlement Servlet Filter.
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
id="WebApp_ID" version="2.5">
<display-name>Entitlement_Sample_WebApp</display-name>
<!-- The scope in which the subject would be available. Legal values are basicAuth, request-param, request-attribute, session -->
<!-- This param is optional. If not provided would be set to default value -->
<context-param>
<param-name>subjectScope</param-name>
<param-value>basicAuth</param-value>
</context-param>
<!-- The name of the identifier by which to identify the subject -->
<!-- This param is Mandatory. Should be provided -->
<context-param>
<param-name>subjectAttributeName</param-name>
<param-value>username</param-value>
</context-param>
<!-- The username to perform EntitlementService query-->
<!-- This param is Mandatory. Should be provided -->
<context-param>
<param-name>userName</param-name>
<param-value>admin</param-value>
</context-param>
<!-- The password to perform EntitlementService query -->
<!-- This param is Mandatory. Should be provided -->
<context-param>
<param-name>password</param-name>
<param-value>admin</param-value>
</context-param>
<!-- The URL to perform EntitlementService query-->
<!-- This param is Mandatory. Should be provided in this format -->
<!--If the transport type is SOAP give the url like https://localhost:9443/services/-->
<!--If the transport type is Thrift give the url like https://localhost:9443/-->
<context-param>
<param-name>remoteServiceUrl</param-name>
<param-value>https://localhost:9443/services/</param-value>
</context-param>
<!-- EntitlementFilter Settings -->
<filter>
<filter-name>EntitlementFilter</filter-name>
<filter-class>org.wso2.carbon.identity.entitlement.filter.EntitlementFilter</filter-class>
<!--Client Class that extends AbstractEntitlementServiceClient. Legal values are basicAuth, soap and thrift.Default is 'thrift'.-->
<init-param>
<param-name>client</param-name>
<param-value>basicAuth</param-value>
</init-param>
<!--Decision caching at PEPProxy. Legal values are simple and carbon.This parameter is optional.
If not specified no caching is done.-->
<init-param>
<param-name>cacheType</param-name>
<param-value>simple</param-value>
</init-param>
<!--Maximum number of cached entries. Legal values are between 0 and 10000 .Only works with caching.-->
<init-param>
<param-name>maxCacheEntries</param-name>
<param-value>1000</param-value>
</init-param>
<!-- Time interval for which cached entry is valid. Only works with simple cache type. -->
<init-param>
<param-name>invalidationInterval</param-name>
<param-value>100000</param-value>
</init-param>
<!-- URL ro redirect to if authorization fails -->
<!-- This param is Mandatory. Should be provided -->
<init-param>
<param-name>authRedirectUrl</param-name>
<param-value>/index.jsp</param-value>
</init-param>
<!-- This will be used if the transport type is thrift. This is mandatory -->
<init-param>
<param-name>thriftHost</param-name>
<param-value>localhost</param-value>
</init-param>
<!-- This will be used if the transport type is thrift. This is optional. If not provided would be set to default value -->
<init-param>
<param-name>thriftPort</param-name>
<param-value>10500</param-value>
</init-param>
</filter>
<!-- Filter mappings used to configure URLs that need to be authorized -->
<filter-mapping>
<filter-name>EntitlementFilter</filter-name>
<url-pattern>/protected.jsp</url-pattern>
</filter-mapping>
<!-- Filter mappings used to configure URLs that need to be authorized -->
<filter-mapping>
<filter-name>EntitlementFilter</filter-name>
<url-pattern>/other.jsp</url-pattern>
</filter-mapping>
<!-- Mandatory mapping that needs to be present to work with PEP cache update authorization-->
<filter-mapping>
<filter-name>EntitlementFilter</filter-name>
<url-pattern>/updateCacheAuth.do</url-pattern>
<dispatcher>FORWARD</dispatcher>
</filter-mapping>
<servlet>
<servlet-name>EntitlementCacheUpdateServlet</servlet-name>
<servlet-class>org.wso2.carbon.identity.entitlement.filter.EntitlementCacheUpdateServlet
</servlet-class>
<!-- HTTPS port of the web container used when redirecting request to come over https port for cache update authentication -->
<init-param>
<param-name>httpsPort</param-name>
<param-value>9453</param-value>
</init-param>
<!-- Authentication mode for cache update. Legal values are webapp and wso2is -->
<init-param>
<param-name>authentication</param-name>
<param-value>webapp</param-value>
</init-param>
<!-- Authentication page used for cache update authentication. Legal values are default and custom -->
<init-param>
<param-name>authenticationPage</param-name>
<param-value>default</param-value>
</init-param>
<!-- Authentication page URL used for cache update authentication. Works only with custom for authenticationPage -->
<init-param>
<param-name>authenticationPageUrl</param-name>
<param-value>/updateCache.html</param-value>
</init-param>
</servlet>
<!-- Servlet mapping needed for cache update authentication -->
<servlet-mapping>
<servlet-name>EntitlementCacheUpdateServlet</servlet-name>
<url-pattern>/updateCache.do</url-pattern>
</servlet-mapping>
</web-app>
Running The Entitlement Servlet Filter Sample
Pre Requests
- Start an instance of WSO2 IS.
- Import the sample XACML policy to the IS, which is given in sample directory's src/main/resources.
- Please see the web.xml file given in the sample directory's src/main/webapp/WEB-INF/web.xml .
- If you are running WSO2 IS in a configuration other than default please edit the web.xml as needed.
- Apache Ant is installed in your system.
Running the Sample
The base directory of this sample has the build.xml file which is used to build the necessary Web App and to deploy it in WSO2 App Server.
- To build and deploy the sample, type "ant"
- Start the App Server and access the Management Console. Go to the webapp service listing page. You will see the deployed service.
- You have to run the run-client.sh or run-client.bat script. It has all the arguments and classpaths configured to run the sample.
- In the console it will show the result for several Entitlement Decision Scenarios.
Output Of the Sample
***********Starting the Entitlement Servlet Filter Sample************ Sending Request For a Web Page Which Requires Authorization Subject : admin Resource : /Entitlement_Sample_WebApp/protected.jsp Action : GET Environment : Not Specified ***Response BEGIN *** <html> <head><title>Protected Page</title></head> <body>Only Authorized Users Can View This</body> </html> ***Response END *** Sending Request For a Web Page Which Not Requires Authorization Subject : admin Resource : /Entitlement_Sample_WebApp/index.jsp Action : GET Environment : Not Specified ***Response BEGIN *** <html> <head><title>Index Page</title></head> <body>Anybody Can Access This Page....</body> </html> ***Response END *** Sending Request For a Web Page Which Requires Authorization with False Subject NAME Subject : andunslg Resource : /Entitlement_Sample_WebApp/protected.jsp Action : GET Environment : Not Specified ***Response BEGIN *** Server returned HTTP response code: 401 for URL: http://localhost:9763/Entitlement_Sample_WebApp/protected.jsp ***Response END *** Sending Request For a Web Page Which Requires Authorization with False Action Subject : admin Resource : /Entitlement_Sample_WebApp/protected.jsp Action : POST Environment : Not Specified ***Response BEGIN *** <html> <head><title>Protected Page</title></head> <body>Only Authorized Users Can View This</body> </html> ***Response END *** Sending Request For a Web Page Which Requires Authorization But Policy is not defined Subject : admin Resource : /Entitlement_Sample_WebApp/other.jsp Action : GET Environment : Not Specified ***Response BEGIN *** <html> <head><title>Index Page</title></head> <body>Anybody Can Access This Page....</body> </html> ***Response END *** ***********Ending the Entitlement Servlet Filter Sample************
In this sample we create a Web App with Entitlement Servlet Filter engaged. All the dependencies are packed in to the lib. So this sample can be run in any other webapp container. You have to simply host the Web App in the container and edit the pom.xml to give the URL of the web application. Thereafter, you can check the functionality.