Using CAS with Java

This document is an evolution of Drew Mazurek's Using CAS With Java HTML / Word document. It provides information about the Java Filter, JSP Tag, and core Java objects provided in the Java CAS Client.

CAS Filter

The CAS filter is the simplest way of CAS-protecting your Java Servlets application.

Configuring CASFilter

Just a few lines of XML need to be added to your web application's deployment descriptor (web.xml):

<web-app>
  ...
  <filter>
    <filter-name>CAS Filter</filter-name>
    <filter-class>edu.yale.its.tp.cas.client.filter.CASFilter</filter-class>
    <init-param>
      <param-name>edu.yale.its.tp.cas.client.filter.loginUrl</param-name>
      <param-value>https://secure.its.yale.edu/cas/login</param-value>
    </init-param>
    <init-param>
      <param-name>edu.yale.its.tp.cas.client.filter.validateUrl</param-name>
      <param-value>https://secure.its.yale.edu/cas/serviceValidate</param-value>
    </init-param>
    <init-param>
      <param-name>edu.yale.its.tp.cas.client.filter.serverName</param-name>
      <param-value>your server name and port (e.g., www.yale.edu:8080)</param-value>
    </init-param>
  </filter>

  <filter-mapping>
    <filter-name>CAS Filter</filter-name>
    <url-pattern>/cas-protected/*</url-pattern>
  </filter-mapping>
  ...
</web-app>

In this case, any URL beneath /webapp/cas-protected would require a CAS login. If you want to protect your entire web application, you can simply put /* for the URL pattern:

<filter-mapping>
    <filter-name>CAS Filter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

The serverName initialization parameter does not require a port number if you are using the standard HTTP port (80).

You can specify other initialization parameters to configure the behavior of the filter:

Required CASFilter init-params

init-param name	usage
edu.yale.its.tp.cas.client.filter.loginUrl	The URL whereat CAS offers its Login page. e.g. https://secure.its.yale.edu/cas/login
edu.yale.its.tp.cas.client.filter.validateUrl	The URL whereat CAS offers its service ticket or proxy ticket validation service. e.g. https://secure.its.yale.edu/cas/serviceValidate or https://secure.its.yale.edu/cas/proxyValidate . Must be a proxyValidate service if you intend to accept any proxy tickets.
edu.yale.its.tp.cas.client.filter.serverName	This parameter specifies the server name and port of the service being filtered (not of the CAS Server itself). E.g., www.yale.edu:8080 Either this parameter or the serviceUrl parameter must be set.
edu.yale.its.tp.cas.client.filter.serviceUrl	This parameter replaces the serverName parameter above. It becomes the URL that CAS redirects to after login. If you have one specific point of entry to your web application and you want all logins to proceed through that page, you would specify the full URL of that page here. Either this parameter or the serverName parameter must be set.

Optional CASFilter init-params

init-param	usage
edu.yale.its.tp.cas.client.filter.proxyCallbackUrl	to obtain a Proxy Granting Ticket and thereby have your application proxy authentication to other services, you'll need to specify an http: URL where you'd like PGT, PGTIOU pairs sent. This will typically be a URL you've mapped to an instance of the ProxyTicketReceptor servlet.
edu.yale.its.tp.cas.client.filter.authorizedProxy	to allow the filter to accept proxy tickets, you need to specify valid proxies through which the authorization must have proceeded. This initialization parameter accepts a whitespace-delimited list of valid proxy URLs. Only one URL needs to match for the login to be successful. Note that if you do want to accept proxy tickets, you will have to change the validateUrl above to proxyValidate rather than serviceValidate
edu.yale.its.tp.cas.client.filter.renew	if set to the string, true, this is the equivalent of authenticating a ticket with renew=true passed as a parameter. This may be used for high-security applications where the user must enter his/her credentials again before accessing the filtered URLs.
edu.yale.its.tp.cas.client.filter.wrapRequest	if set to the string "true" the CASFilter will wrap the request such that calls to getRemoteUser() return the authenticated username.
edu.yale.its.tp.cas.client.filter.gateway	see gateway

Consuming the results of CASFilter

Once the user has logged into your application through the filter, the application may access the user's name through the session attribute, edu.yale.its.tp.cas.client.filter.user, or if you import edu.yale.its.tp.cas.client.filter.CASFilter in your JSP or servlet, simply CASFilter.CAS_FILTER_USER.

Accessing the authenticated username from Java

// either of these will work:
session.getAttribute(CASFilter.CAS_FILTER_USER);
session.getAttribute("edu.yale.its.tp.cas.client.filter.user");

Accessing the authenticated username via JSTL

<c:out value="${sessionScope[CAS:'edu.yale.its.tp.cas.client.filter.user']}"/>

Additionally, the client application may access a CASReceipt JavaBean-style object which exposes the username as well as additional information about the successful authentication, in the session attribute edu.yale.its.tp.cas.client.filter.receipt .

// either of these will work:
session.getAttribute(CASFilter.CAS_FILTER_RECEIPT);
session.getAttribute("edu.yale.its.tp.cas.client.filter.receipt");

Session attributes set by CASFilter

Session attribute	usage
edu.yale.its.tp.cas.client.filter.user	String representing the authenticated NetID
edu.yale.its.tp.cas.client.filter.receipt	CASReceipt representing the results of CAS authentication. Use this object to programmatically access the proxy chain, whether the authentication was required to have been by presentation of primary credentials, etc.

CAS Tag Library

The CAS Tag Library is a another way to authenticate users' access to JSP pages. JSP Tags cannot be used in servlets, so if you need CAS protection within a servlet environment, you can use either the CAS Filter or the CAS Java objects (see below); the former is recommended.

To use the tag library, once casclient.jar is installed in your web application's /WEB-INF/lib directory, you need to add the following to the top of a JSP page you wish to protect:

<%@ taglib uri="http://www.yale.edu/its/tp/cas/version2" prefix="cas" %>
<cas:auth var="netID" scope="session">
  <cas:loginUrl>https://secure.its.yale.edu/cas/login</cas:loginUrl>
  <cas:validateUrl>https://secure.its.yale.edu/cas/proxyValidate</cas:validateUrl>
  <cas:authorizedProxy>https://authorized-proxy1</cas:authorizedProxy>
  <cas:authorizedProxy>https://authorized-proxy2</cas:authorizedProxy>
  ...
  <cas:service>http://service-url</cas:service>
</cas:auth>
...

<html>
<body>
<p>Welcome, <%= session.getAttribute("netID") %>!</p>
</body>
</html>

The user will not see any part of the page past the <cas:auth /> tags until he/she has logged in. If the user hasn't logged in yet, a redirect to the CAS login page will be performed.

Also provided with the CAS Tag Library is a logout tag:

<%@ taglib uri="http://www.yale.edu/its/tp/cas/version2" prefix="cas" %>
<%-- first destroy the web application's session --%>
<%   session.invalidate(); %>
<%-- then logout of CAS --%>
<cas:logout var="netID" scope="session"
    logoutUrl="https://secure.its.yale.edu/cas/logout" />

CAS Java Objects

You may also authenticate users "manually" using the CAS Java objects. In this case, you would instantiate a new ServiceTicketValidator or ProxyTicketValidator. Notice that in the example below, the page already expects to receive a ticket parameter (this is the servlet that CAS returned to after the user logged in). If this servlet was accessed directly by a user, it would need to check that the request parameter, ticket, was not null. If it was null, the servlet would need to redirect to the CAS login page manually.

ServiceTicketValidator:

import edu.yale.its.tp.cas.client.*;

...
String user = null;
String errorCode = null;
String errorMessage = null;
String xmlResponse = null;

/* instantiate a new ServiceTicketValidator */
ServiceTicketValidator sv = new ServiceTicketValidator();

/* set its parameters */
sv.setCasValidateUrl("https://secure.its.yale.edu/cas/serviceValidate");
sv.setService(urlOfThisService);
sv.setServiceTicket(request.getParameter("ticket"));

/*
 * If we want to be able to acquire proxy tickets (requires callback servlet to be set up 
 * in web.xml - see below)
 */

String urlOfProxyCallbackServlet = "https://portal.yale.edu/CasProxyServlet";

sv.setProxyCallbackUrl(urlOfProxyCallbackServlet);

/* contact CAS and validate */
sv.validate();

/* if we want to look at the raw response, we can use getResponse() */
xmlResponse = sv.getResponse();

/* read the response */

// Yes, this method is misspelled in this way 
// in the ServiceTicketValidator implementation. 
// Sorry.
if(sv.isAuthenticationSuccesful()) {
    user = sv.getUser();
} else {
    errorCode = sv.getErrorCode();
    errorMessage = sv.getErrorMessage();
    /* handle the error */
}

/* The user is now authenticated. */

/* If we did set the proxy callback url, we can get proxy tickets with: */


String urlOfTargetService = "http://hkg2.its.yale.edu/someApp/portalFeed";

String proxyTicket =
    edu.yale.its.tp.cas.proxy.ProxyTicketReceptor.getProxyTicket(
        sv.getPgtIou(),urlOfTargetService);

ProxyTicketValidator

The proxy ticket validator is almost identical, except it allows you to validate service tickets or proxy tickets. This class contains one additional method, getProxyList(), which accesses the list of URLs through which the authentication was proxied.

import edu.yale.its.tp.cas.client.*;

...

String user = null;
String errorCode = null;
String errorMessage = null;
String xmlResponse = null;
List proxyList = null;

/* instantiate a new ProxyTicketValidator */
ProxyTicketValidator pv = new ProxyTicketValidator(); 

/* set its parameters */
pv.setCasValidateUrl("https://secure.its.yale.edu/cas/proxyValidate");
pv.setService(urlOfThisService);
pv.setServiceTicket(request.getParameter("ticket")); 

/*
 * If we want to be able to acquire proxy tickets (requires callback servlet to be set up 
 * in web.xml -- see below)
 */

String urlOfProxyCallbackServlet = "https://portal.yale.edu/CasProxyServlet";

pv.setProxyCallbackUrl(urlOfProxyCallbackServlet); 

/* contact CAS and validate */
pv.validate();

/* if we want to look at the raw response, we can use getResponse() */
xmlResponse = pv.getResponse(); 

/* read the response */
// Yes, this method is misspelled in this way 
// in the ServiceTicketValidator implementation. 
// Sorry.
if(pv.isAuthenticationSuccesful()) {
    user = pv.getUser();
    proxyList = pv.getProxyList();
} else {
    errorCode = pv.getErrorCode();
    errorMessage = pv.getErrorMessage();
    /* handle the error */
}

/* The user is now authenticated. */

/* If we did set the proxy callback url, we can get proxy tickets with this method call: 
 */

String urlOfTargetService = "http://hkg2.its.yale.edu/someApp/portalFeed";

String proxyTicket =
    edu.yale.its.tp.cas.proxy.ProxyTicketReceptor.getProxyTicket(
        pv.getPgtIou(),urlOfTargetService);

ProxyTicketReceptor

In order to obtain proxy tickets, the proxy callback listener must be set up as a servlet in the application's web.xml:

<web-app>

  ...
  <servlet>
    <servlet-name>ProxyTicketReceptor</servlet-name>
    <servlet-class>edu.yale.its.tp.cas.proxy.ProxyTicketReceptor</servlet-class>
  </servlet>

 

  <servlet-mapping>
    <servlet-name>ProxyTicketReceptor</servlet-name>
    <url-pattern>/CasProxyServlet</url-pattern>
  </servlet-mapping>
  ...

</webapp>