Application security - the art of applications defending themselves - represents an important line of defence in an overall in-depth security strategy. Web applications that follow the Model-View-Controller (MVC) architecture can, and should, have security implemented on all three layers. Normally it's the controller component that handles page authorization in MVC, the view layer that hides controls and information based on user authorization, and the model that enforces the business rules and input validation. However, it's up to the developer, based on an individual security policy and the programming technology used, to decide where to put security. Using pluggable validator components in JavaServer Faces (JSF), for example, developers may decide to verify user input on the view layer as well as on the model layer.

 JavaServer Faces, the new J2EE standard for building feature-rich Web applications with JEE 1.5, has few integrated security features. JSF generously delegates the task of implementing application security such as page authorization to the application developer, leaving many developers pondering where to start, where best to put security, and which security technology to choose.

This article aims to answer such questions for authorization in JavaServer Faces, demonstrating how a custom PhaseListener that uses J2EE container-managed security can be used to implement access control for JSF pages. Besides page authorization, the security PhaseListener supports protocol switching between HTTP and HTTPS, a common requirement of applications that work with sensitive data on a Web page.

The J2EE Security Choices
The J2EE platform provides two built-in security technologies for the application developer to use: the Java Authentication and Authorization Service (JAAS) and container-managed security, also known as J2EE security.

The Java Authentication and Authorization Service is a J2SE 1.4 security standard designed for the Java desktop that's also used as an implementation technology for security in J2EE. The JAAS authentication infrastructure is built as a Java version of the Pluggable Authentication Module (PAM) architecture that allows one or more authentication providers to be used for user identification. Before JAAS, the Java 2 security platform was code-centric, determining access privileges based solely on the location of the Java sources. Using JAAS, Java security now also looks at the authenticated user when evaluating access control to resources. JAAS's benefit is its ability to implement fine-grained access control through external Java permission classes, which associate users with a list of resources and allowed actions.

Authentication and authorization in J2EE security is configured declaratively in the application's web.xml deployment descriptor and handled by the J2EE container at runtime. Working with APIs defined in the J2EE servlet standard, application developers don't have to worry about the implementation of security in a container. In container-managed security, authorization is enforced on URL patterns, which are absolute or relative URLs. This however also means that authorization is only enforced on requests that are initiated by the client, not as server-side forward requests.

Ease of use, the clean separation of security definition and application code, and portability across application servers are the main reasons for the wide adoption of container-managed security among business application developers. J2EE security is sufficient to implement many common security use cases. As a reflection of its popularity and its portability, container-managed security is used in the code examples of this article to illustrate effective page authorization in JavaServer Faces.

Container-Managed Security in J2EE
In container-managed security, a user is granted access to protected URL resources through security roles defined in the web.xml deployment descriptor. Security roles in J2EE are logical names used in Web applications that are mapped during or after deployment to user groups that exist on the target application server platform.

Listing 1 Web.xml excerpt granting the app_user security role access to the protected URL resource /faces/protected/*

<security-constraint>
    <Web-resource-collection>
    <Web-resource-name>Members</Web-resource-name>
    <url-pattern>/faces/protected/*</url-pattern>
    </Web-resource-collection>
    <auth-constraint>
       <role-name>app_user</role-name>
    </auth-constraint>
</security-constraint>
...
<security-role>
    <role-name>app_user</role-name>
</security-role>

To access a protected application resource, Web application users must first authenticate, which in container-managed security is handled by the J2EE container. Either the application developer or the application deployer configures the type of authentication in the web.xml deployment descriptor.

Listing 2 Basic authentication defined for the jazn.com realm

<login-config>
     <auth-method>BASIC</auth-method>
     <realm-name>jazn.com</realm-name>
</login-config>

To check authorization programmatically in an J2EE application - like in JavaServer Faces - application developers use the isUserInRole method in the servlet API. This isUserInRole method is also exposed via a convenience method in JavaServer Faces through the static FacesContext class. Role names referenced in application code ought to be mapped to roles defined in the web.xml file using the <security-role-ref> element if the role names don't match. Using the <security-role-ref> element, developers don't have to be aware of the security role names that exist in the web.xml descriptor when developing an application.

Listing 3 Mapping the "user" role name used in the application code to the security role name "manager_role" defined in the web.xml file

<security-role-ref>
     <role-name>user</role-name>
     <role-link>app_user</role-link>
</security-role-ref>

If the authenticated user isn't authorized to access the requested URL resource, the J2EE container responds with HTTP error 403, indicating a bad request. A HTTP error 401 is returned if a user cancels the authentication process. HTTP error codes and Java exceptions are handled declaratively in the web.xml file using the <error-page> element.

Listing 4 Redirecting a request in response to unauthorized page access handling error code 403 and 401

<error-page>
     <error-code>403</error-code>
     <location>Error.jsp</location>
</error-page>
<error-page>
     <error-code>401</error-code>
     <location>Logon_cancelled.jsp</location>
</error-page>

If SSL is required to ensure secure communication when accessing a specific Web resource, the <security-constraint> element added for a protected resource contains an additional <user-data-constraint> element. Setting the transport guarantee to "confidential" indicates that SSL is required.