WAR Overlay Installation

CAS installation is a fundamentally source-oriented process, and we recommend a WAR overlay (1) project to organize customizations such as component configuration and UI design. The output of a WAR overlay build is a cas.war file that can be deployed to a servlet container like Apache Tomcat.


See this guide to learn more.

What is a WAR Overlay?

Overlays are a strategy to combat repetitive code and/or resources. Rather than downloading the CAS codebase and building from source, overlays allow you to download a pre-built vanilla CAS web application server provided by the project itself and override/insert specific behavior into it. At build time, the build installation process will attempt to download the provided binary artifact first. Then the tool will locate your configuration files and settings made available inside the same project directory and will merge those into the downloaded artifact in order to produce one wholesome archive (i.e. cas.war) . Overridden artifacts may include resources, java classes, images, CSS and javascript files. In order for the merge process to successfully execute, the location and names of the overridden artifacts locally must EXACTLY match that of those provided by the project inside the originally downloaded archive. Java code in the overlay project’s src/main/java folder and resources in src/main/resources will end up in the WEB-INF\classes folder of cas.war and they will be loaded by the classloader instead of resources with the same names in jar files inside WEB-INF\lib.

It goes without saying that while up-front ramp-up time could be slightly complicated, there are significant advantages to this approach:

  1. There is no need to download/build from the source.
  2. Upgrades are tremendously easier in most cases by adjusting the build script to download the newer CAS release.
  3. Rather than hosting the entire software source code, as the deployer you ONLY keep your own local customizations which makes change tracking much easier.
  4. Tracking changes inside a source control repository is very lightweight, again because only relevant changes (and not the entire software) is managed.

Managing Overlays

Most if not all aspects of CAS can be controlled by adding, removing, or modifying files in the overlay; it’s also possible and indeed common to customize the behavior of CAS by adding third-party components that implement CAS APIs as Java source files or dependency references.

The process of working with an overlay can be summarized in the following steps:

  • Start with and build the provided basic vanilla build/deployment.
  • Identify the artifacts from the produced build that need changes. These artifacts are generally produced by the build in the build directory for Gradle. Use the gradle explodeWar task.
  • Copy the identified artifacts from the identified above directories over to the src/main/resources directory.
    1. Create the src/main/resources directories, if they don’t already exist.
    2. Copied paths and file names MUST EXACTLY MATCH their build counterparts, or the change won’t take effect. See the table below to understand how to map folders and files from the build to src.
  • After changes, rebuild and repeat the process as many times as possible.
  • Double check your changes inside the built binary artifact to make sure the overlay process is working.
Be Exact

Do NOT copy everything produced by the build. Attempt to keep changes and customizations to a minimum and only grab what you actually need. Make sure the deployment environment is kept clean and precise, or you incur the risk of terrible upgrade issues and painful headaches.

CAS WAR Overlays

CAS WAR overlay projects described below are provided for reference and study.

CAS Overlay Initializr

Apereo CAS Initializr is a relatively new addition to the Apereo CAS ecosystem that allows you as the deployer to generate CAS WAR Overlay projects on the fly with just what you need to start quickly.

To learn more about the initializr, please review this guide.

CAS Overlay Template

The CAS WAR overlay template project can be bootstrapped and generated via the CAS Initializr.

The WAR overlay also provides additional tasks to explode the binary artifact first before re-assembling it again. You may need to do that step manually yourself to learn what files/directories need to be copied over to the source directory.

Note: Do NOT ever make changes in the above-noted build directory. The changeset will be cleaned out and set back to defaults every time you do a build. Put overlaid components inside the source directory and/or other instructed locations to avoid surprises.

Dockerized Deployment

See this guide for more info.

Servlet Container

CAS can be deployed to a number of servlet containers. See this guide for more info.

Custom and Third-Party Source

It is common to customize or extend the functionality of CAS by developing Java components that implement CAS APIs or to include third-party source by dependency references. Including third-party source is trivial; include the relevant dependency in the overlay build.gradle file.

Stop Coding

Overlaying or modifying CAS internal components and classes, unless ABSOLUTELY required, should be a last resort and is generally considered a misguided malpractice. Where possible, avoid making custom changes to carry the maintenance burden solely on your own. You will risk the stability and security of your deployment. If the enhancement case is attractive or modest, contribute back to the project. Stop writing code, or write it where it belongs.

In order to include custom Java source, it should be included under a src/main/java directory in the overlay project source tree.

├── src
│   ├── main
│   │   ├── java
│   │   │   └── edu
│   │   │       └── sso
│   │   │           └── middleware
│   │   │               └── cas
│   │   │                   ├── audit
│   │   │                   │   ├── CompactSlf4jAuditTrailManager.java
│   │   │                   ├── authentication
│   │   │                   │   └── principal
│   │   │                   │       └── UsernamePasswordCredentialsToPrincipalResolver.java
│   │   │                   ├── services
│   │   │                   │   └── JsonServiceRegistryDao.java
│   │   │                   ├── util
│   │   │                   │   └── X509Helper.java
│   │   │                   └── web
│   │   │                       ├── HelpController.java
│   │   │                       ├── flow
│   │   │                       │   ├── AbstractForgottenCredentialAction.java
│   │   │                       └── util
│   │   │                           ├── ProtocolParameterAuthority.java

Dependency Management

Each release of CAS provides a curated list of dependencies it supports. In practice, you do not need to provide a version for any of these dependencies in your build configuration as the CAS distribution is managing that for you. When you upgrade CAS itself, these dependencies will be upgraded as well in a consistent way.

The curated list of dependencies contains a refined list of third party libraries. The list is available as a standard Bills of Materials (BOM). Not everyone likes inheriting from the BOM. You may have your own corporate standard parent that you need to use, or you may just prefer to explicitly declare all your configuration.

To take advantage of the CAS BOM, please see this guide.

(1) WAR Overlays