Extreme Java

Still working on the application I describe in my previous post, I started to integrate it to use JAAS. It is a Struts-based system running in a Tomcat server. The login was an Struts Action, and a RequestProcessor took care of redirecting to login page.

It was pretty easy the conversion to JAAS:

1. I developed a new Realm for Tomcat. It was just a matter of extend the RealmBase class and override the authenticate method. This step could be skipped if my employer’s LDAP server accepted anonymous search - JNDIRealm can do this job;
2. With the Realm ready, add it to the application’s context.xml (NetBeans users will find it inside META-INF folder of the project);
3. Next step was to make a “public access” version of the application. Every code that does the authentication and authorization was removed, except the dynamic menu;
4. The dynamic menu was changed to use the request.isUserInRole method. For some reason, this property can’t be accessed by EL. I expected something like “request.userInRole[’role’]”, but it didn’t work;
5. The logged user can be retrieved with either request.getUserPrincipal() or the EL “pageContext.request.userPrincipal”;
6. Now, it is just a matter of adding every Struts action to security constraints in web.xml. In NetBeans, it’s an easy-to-use visual editor. Here is a snippet:

   <security-constraint>
     <web-resource-collection>
       <web-resource-name>SecurePages</web-resource-name>
       <description>My secret pages</description>
       <url-pattern>/secure.do</url-pattern>
       <http-method>GET</http-method>
     </web-resource-collection>
   
     <auth-constraint>
       <description>Allowed roles</description>
       <role-name>power_user</role-name>
     </auth-constraint>
   </security-constraint>

7. The login page, if using FORM-based authentication, is now something like:

   <form action="j_security_check" method="post">
     User: <input type="text" name="j_username"/>
     Password: <input type="password" name="j_password"/>
     <input type="submit" name="btLogin" value="login"/>
   </form>

8. To activate the FORM-based login, this must be added to web.xml:

   <login-config>
     <auth-method>FORM</auth-method>
     <form-login-config>
       <form-login-page>/login.jsp</form-login-page>
       <form-error-page>/login.jsp</form-error-page>
     </form-login-config>
   </login-config>

9. Did you notice the login error page is the same as the login page? To check if the user entered an invalid password, I use:

   <c:if test="${param.btLogin == 'login' and param.j_username <> ''}">
     <c:out value="Invalid username and/or password"/>
   </c:if>

It is a long boilerplate, but steps are the same for every application. Using JAAS instead of programatic authorization makes your system more secure and easier to maintain.