Delegated Authentication Discovery Selection

External identity providers available to CAS are presented to the user and available for discovery and selection using the following strategies.

Remember

If you are interested in supporting discovery of SAML2 identity providers using a discovery service, you may want to take a look at this guide.

The following settings and properties are available from the CAS configuration catalog:

cas.authn.pac4j.core.discovery-selection.json.locationThe location of the resource.

no default

Required

The location of the resource. Resources can be URLs, or files found either on the classpath or outside somewhere in the file system.

In the event the configured resource is a Groovy script, especially if the script is set to reload on changes, you may need to adjust the total number of inotify instances. On Linux, you may need to add the following line to /etc/sysctl.conf: fs.inotify.max_user_instances = 256.

You can check the current value via cat /proc/sys/fs/inotify/max_user_instances.

In situations and scenarios where CAS is able to automatically watch the underlying resource for changes and detect updates and modifications dynamically, you may be able to specify the following setting as either an environment variable or system property with a value of false to disable the resource watcher: org.apereo.cas.util.io.PathWatcherService.

Type: Resource
Default: none
Defined by: Pac4jDelegatedAuthenticationDiscoverySelectionJsonProperties

cas.authn.pac4j.core.discovery-selection.selection-typeIndicate how the selection and presentation of identity providers would be controlled.

MENU

Required

Indicate how the selection and presentation of identity providers would be controlled. Available values are as follows:

MENU: Defined identity providers will be listed for the user to select.
DYNAMIC: Defined identity providers are pre-built first, and one is chosen dynamically at runtime based on user attributes properties, domain identifier, etc.

Type: Pac4jDelegatedAuthenticationDiscoverySelectionProperties.Pac4jDelegatedAuthenticationSelectionTypes
Default: MENU
Defined by: Pac4jDelegatedAuthenticationDiscoverySelectionProperties

cas.authn.pac4j.core.discovery-selection.json.principal-attributeThe name of the principal attribute whose values will be compared against the key pattern defined in the configuration rules.

no default

The name of the principal attribute whose values will be compared against the key pattern defined in the configuration rules. If a match is found, then the provider configuration block will be used as the selected provider. The matching routine will examine all attribute values linked to the principal attribute to find any acceptable match. When this setting left undefined, then the resolved principal id for the given user identifier will be used to locate the provider.

Type: String
Default: none
Defined by: Pac4jDelegatedAuthenticationDiscoverySelectionJsonProperties

Required settings may be needed to activate or affect the feature; review them even when they have a default. Optional settings only need to be set to change a default or to turn on the behavior they control. Third party settings belong to libraries such as Spring Boot that CAS builds on; their own documentation may have more detail.

Notes on configuration

Configuration Metadata

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.

Be Selective

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.

YAGNI

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.

Naming Convention

Property names can be specified in very relaxed terms. For instance cas.someProperty, cas.some-property, 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.

Note

When possible, properties should be stored in lower-case kebab format, such as cas.property-name=value. The only possible exception to this rule is when naming actuator endpoints; The name of the actuator endpoints (i.e. ssoSessions) MUST remain in camelCase mode.

Settings 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.

Validation

Configuration properties are automatically validated on CAS startup to report issues with configuration binding, especially if defined CAS settings cannot be recognized or validated by the configuration schema. Additional validation processes are also handled via Configuration Metadata and property migrations applied automatically on startup by Spring Boot and family.

Indexed Settings

CAS settings able to accept multiple values are typically documented with an index, such as cas.some.setting[0]=value. The index [0] is meant to be incremented by the adopter to allow for distinct multiple configuration blocks.

This is the default and most common strategy that allows external identity providers to be listed on the login page, allowing the user to order one from the menu and select one from the list of options.

Rather than listing all available identity providers, this option allows CAS to auto-select the appropriate identity provider in a dynamic fashion using pre-defined rules and conditions and based on the user identifiers such as username, email address, etc. For example, once the user providers their identifier, i.e. casuser@example.org, the discovery strategy can try to select the correct identity provider based on the email domain.

JSON Rules

By default, the selection rules and conditions can be specified in a JSON file with the following structure:

{
    "@class" : "java.util.HashMap",
    "<key-pattern>" : {
      "@class" : "org.apereo.cas.pac4j.discovery.DelegatedAuthenticationDynamicDiscoveryProvider",
      "clientName" : "SAML2Client",
      "order": 0
    }
}

The following parameters are available to the JSON resource:

Parameter	Description
`<key-pattern>`	Regular expression pattern matched against the user identifier (or principal attribute values) to locate the provider. i.e. `.+@example.org`.
`clientName`	The client name that should be used for this match, found and defined in CAS configuration.
`order`	The selection sorting order, used to properly sequence and prioritize entries in case there is overlap.

If you wish to create your own strategy to dynamically locate identity providers for delegated authentication discovery, you will need to design a component and register it with CAS as such:

@Bean
public DelegatedAuthenticationDynamicDiscoveryProviderLocator delegatedAuthenticationDynamicDiscoveryProviderLocator() {
    return new CustomDelegatedAuthenticationDynamicDiscoveryProviderLocator();
}

See this guide to learn more about how to register configurations into the CAS runtime.