Authentication Interrupt

CAS has the ability to pause and interrupt the authentication flow to reach out to external services and resources, querying for status and settings that would then dictate how CAS should manage and control the SSO session. Interrupt services are able to present notification messages to the user, provide options for redirects to external services, etc. A common use case deals with presenting a bulletin board during the authentication flow to present messages and announcements to select users and then optionally require the audience to complete a certain task before CAS is able to honor the authentication request and establish a session.

In the interrupt flow, CAS is not at the moment reaching back to an external resource acting as an interrupt service to store, track or remember a user’s decision. In other words, we are only dealing with the R (ie. Read) in CRUD. Today’s functionality only deals with inquiring status and reading results solely in read-only mode. Interrupt services are themselves required and encouraged to redirect the audience to external resources where execution of an action resets the interrupt status thereby freeing CAS to proceed forward later on without having to interrupt the authentication flow again.

Configuration

Support is enabled by including the following dependency in the WAR overlay:

1
2
3
4
5

<dependency>
  <groupId>org.apereo.cas</groupId>
  <artifactId>cas-server-support-interrupt-webflow</artifactId>
  <version>${cas.version}</version>
</dependency>

1

implementation "org.apereo.cas:cas-server-support-interrupt-webflow:${project.'cas.version'}"

1
2
3
4
5
6
7
8
9

dependencyManagement {
  imports {
    mavenBom "org.apereo.cas:cas-server-support-bom:${project.'cas.version'}"
  }
}

dependencies {  
  implementation "org.apereo.cas:cas-server-support-interrupt-webflow"
}

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

The configuration settings listed below are tagged as Required in the CAS configuration metadata. This flag indicates that the presence of the setting may be needed to activate or affect the behavior of the CAS feature and generally should be reviewed, possibly owned and adjusted. If the setting is assigned a default value, you do not need to strictly put the setting in your copy of the configuration, but should review it nonetheless to make sure it matches your deployment expectations.

The configuration settings listed below are tagged as Optional in the CAS configuration metadata. This flag indicates that the presence of the setting is not immediately necessary in the end-user CAS configuration, because a default value is assigned or the activation of the feature is not conditionally controlled by the setting value.

  • cas.interrupt.core.trigger-mode=AFTER_AUTHENTICATION

    • Define how interrupt notifications should be triggered in the authentication flow. Available values are as follows:

    • AFTER_AUTHENTICATION: Trigger interrupt notifications and inquiry after authentication events and before single sign-on has been established.
    • AFTER_SSO: Trigger interrupt notifications and inquiry after single sign-on has been established. Interrupt queries that execute after single sign-on cannot control the creation of the SSO session conditionally.

    org.apereo.cas.configuration.model.support.interrupt.InterruptCoreProperties.

    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. 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.

    Validation

    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.

    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.

    Interrupt Payload

    Each interrupt strategy is ultimately tasked to produce a response that contains the following settings:

    Field Description
    message Announcement message to display on the screen.
    links A map of links to display on the screen where key is the link text and value is the destination.
    interrupt true/false to indicate whether CAS should interrupt the authentication flow.
    block true/false to indicate whether CAS should block the authentication flow altogether.
    ssoEnabled true/false to indicate whether CAS should permit the authentication but not establish SSO.
    autoRedirect true/false to indicate whether CAS should auto-redirect to the first provided link.
    autoRedirectAfterSeconds Indicate whether CAS should auto-redirect after the configured number of seconds. The default is -1, meaning delayed redirect functionality should not be executed.

    Interrupt Trigger Modes

    Authentication interrupts and notifications are executed in the overall flow using one of the following strategies. The trigger strategy is defined globally via CAS settings.

    After Authentication

    This is the default strategy that allows the interrupt query to execute after the primary authentication event and before the single sign-on event. This means an authenticated user has been identified by CAS and by extension is made available to the interrupt, and interrupt has the ability to decide whether a single sign-on session can be established for the user.

    Can We SSO Into Links?

    No. The collection of links are just links and are not tied in any way to the CAS authentication sequence, meaning they do not activate a state, transition or view in that sequence to trigger CAS into generating tickets, executing certain actions, etc. Any link in this collection is exactly that; just a link. If a link points to applications that are integrated with CAS, accessing those applications via the link will prompt the user for credentials again specially if single sign-on isn't already established. Remember that interrupt notifications typically execute after the authentication step and before any single sign-on session is created.

    After Single Sign-on

    Alternatively, the interrupt query can execute once the single sign-on session has been established. In this mode, the authenticated user has been identified by CAS and linked to the single sign-on session. Note that interrupt here loses the ability to decide whether a single sign-on session can be established for the user, and interrupt responses indicating this option will have no impact, since the query and interrupt responses happen after the creation of the SSO session.

    Can We SSO Into Links?

    Yes. In this strategy, links to external applications presented by the interrupt response should be able to take advantage of the established single sign-on session.

    Interrupt Strategies

    Interrupt queries can be executed via the following ways:

    Storage Description
    JSON See this guide.
    Regex Attribute See this guide.
    Groovy See this guide.
    REST See this guide.
    Custom See this guide.

    Skipping Interrupts

    Interrupt notifications may be disabled on a per-service basis. A sample JSON file follows:

    1
2
3
4
5
6
7
8
9
10
11
12
13

    {
  "@class" : "org.apereo.cas.services.RegexRegisteredService",
  "serviceId" : "^https://.+",
  "name" : "sample service",
  "id" : 100,
  "properties" : {
    "@class" : "java.util.HashMap",
    "skipInterrupt" : {
      "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
      "values" : [ "java.util.HashSet", [ "true" ] ]
    }
  }
}

    The following properties are available and recognized by CAS for various modules and features:

    Name Default Value Type Group
    skipInterrupt false BOOLEAN INTERRUPTS