Spring Security
21.1 Overview JA-SIG produces an enterprise-wide single sign on system known as CAS. Unlike other initiatives, JA-SIG's Central Authentication Service is open source, widely used, simple to understand, platform independent, and supports proxy capabilities. Spring Security fully supports CAS, and provides an easy migration path from single-application deployments of Spring Security through to multiple-application deployments secured by an enterprise-wide CAS server. You can learn more about CAS at http://www.ja-sig.org/cas. You will also need to visit this site to download the CAS Server files.
21.2 How CAS Works Whilst the CAS web site contains documents that detail the architecture of CAS, we present the general overview again here within the context of Spring Security. Spring Security 3.0 supports CAS 3. At the time of writing, the CAS server was at version 3.3. Somewhere in your enterprise you will need to setup a CAS server. The CAS server is simply a standard WAR file, so there isn't anything difficult about setting up your server. Inside the WAR file you will customise the login and other single sign on pages displayed to users. When deploying a CAS 3.3 server, you will also need to specify an AuthenticationHandler in the deployerConfigContext.xml included with CAS. The AuthenticationHandler has a simple method that returns a boolean as to whether a given set of Credentials is valid. Your AuthenticationHandler implementation will need to link into some type of backend authentication repository, such as an LDAP server or database. CAS itself includes numerous AuthenticationHandlers out of the box to assist with this. When you download and deploy the server war file, it is set up to successfully authenticate users who enter a password matching their username, which is useful for testing. Apart from the CAS server itself, the other key players are of course the secure web applications deployed throughout your enterprise. These web applications are known as "services". There are two types of services: standard services and proxy services. A proxy service is able to request resources from other services on behalf of the user. This will be explained more fully later.
21.3 Configuration of CAS Client The web application side of CAS is made easy due to Spring Security. It is assumed you already know the basics of using Spring Security, so these are not covered again below. We'll assume a namespace based configuration is being used and add in the CAS beans as required. You will need to add a ServiceProperties bean to your application context. This represents your CAS service:
<bean id="serviceProperties"
3.0.5.RELEASE
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