CAS uses Spring Webflow to do script processing of login and logout protocols. Spring Web Flow builds on Spring MVC and allows implementing the “flows” of a web application. A flow encapsulates a sequence of steps that guide a user through the execution of some business task. It spans multiple HTTP requests, has state, deals with transactional data, is reusable, and may be dynamic and long-running in nature. Each flow may contain among many other settings the following major elements:
- Actions: components that describe an executable task and return back a result
- Transitions: Routing the flow from one state to another; Transitions may be global to the entire flow.
- Views: Components that describe the presentation layer displayed back to the client
- Decisions: Components that conditionally route to other areas of flow and can make logical decisions
Spring Web Flow presents CAS with a pluggable architecture where custom actions, views and decisions may be injected into the flow to account for additional use cases and processes. Note that to customize the webflow, one must possess a reasonable level of understanding of the webflow’s internals and injection policies. The intention of this document is NOT to describe Spring Web Flow, but merely to demonstrate how the framework is used by CAS to carry out various aspects of the protocol and business logic execution.
See this guide for more info.
Webflow Auto Configuration
Most CAS modules, when declared as a dependency, attempt to autoconfigure the CAS webflow to suit their needs. This practically means that the CAS adopter would no longer have to manually massage the CAS webflow configuration, and the module automatically takes care of all required changes. While this is the default behavior, it is possible that you may want to manually handle all such changes. For doing so, you will need to disable the CAS auto-configuration of the webflow.
The following settings and properties are available from the CAS configuration catalog:
Whether webflow auto-configuration should be enabled.
The order in which the webflow is configured.
The collection of configuration properties listed in this section are automatically generated from the CAS source and components that contain the actual field definitions, types, descriptions, modules, etc. This metadata may not always be 100% accurate, or could be lacking details and sufficient explanations.
This section is meant as a guide only. Do NOT copy/paste the entire collection of settings into your CAS configuration; rather pick only the properties that you need. Do NOT enable settings unless you are certain of their purpose and do NOT copy settings into your configuration only to keep them as reference. All these ideas lead to upgrade headaches, maintenance nightmares and premature aging.
Note that for nearly ALL use cases, declaring and configuring properties listed here is sufficient. You should NOT have to explicitly massage a CAS XML/Java/etc configuration file to design an authentication handler, create attribute release policies, etc. CAS at runtime will auto-configure all required changes for you. If you are unsure about the meaning of a given CAS setting, do NOT turn it on without hesitation. Review the codebase or better yet, ask questions to clarify the intended behavior.
Property names can be specified in very relaxed terms. For instance
cas.some_property are all valid names. While all forms are accepted by CAS, there are certain components (in CAS and other frameworks used) whose activation at runtime is conditional on a property value, where this property is required to have been specified in CAS configuration using kebab case. This is both true for properties that are owned by CAS as well as those that might be presented to the system via an external library or framework such as Spring Boot, etc. When possible, properties should be stored in
lower-case kebab format, such as
cas.property-name=value.S ettings and properties that are controlled by the CAS platform directly always begin with the prefix
cas. All other settings are controlled and provided to CAS via other underlying frameworks and may have their own schemas and syntax. BE CAREFUL with the distinction. Unrecognized properties are rejected by CAS and/or frameworks upon which CAS depends. This means if you somehow misspell a property definition or fail to adhere to the dot-notation syntax and such, your setting is entirely refused by CAS and likely the feature it controls will never be activated in the way you intend.
Configuration properties are automatically validated on CAS startup to report issues with configuration binding, specially if defined CAS settings cannot be recognized or validated by the configuration schema. The validation process is on by default and can be skipped on startup using a special system property
SKIP_CONFIG_VALIDATION that should be set to
true. Additional validation processes are also handled via Configuration Metadata and property migrations applied automatically on startup by Spring Boot and family.
CAS settings able to accept multiple values are typically documented with an index, such as
cas.some.setting=value. The index
 is meant to be incremented by the adopter to allow for distinct multiple configuration blocks.
Only attempt to modify the Spring webflow configuration files by hand when/if absolutely necessary and the change is rather minimal or decorative. Extensive modifications of the webflow, if not done carefully may severely complicate your deployment and future upgrades. If reasonable, consider contributing or suggesting the change to the project and have it be maintained directly.
CAS by default is configured to hot reload changes to the Spring webflow configuration.
If you want to learn how to modify and extend the CAS authentication flows, please see this guide.
The following endpoints are provided by CAS: