APEREO CASDocumentation

Enterprise Authentication for All Earthlings and Beyond

Identity, Single Sign-On and Access Management
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Heimdall Authorization

Heimdall is a simple rule-based authorization engine whose main responsibility is to accept an authorization request in form of an HTTP payload and return a decision whether the request is allowed or denied in form of an HTTP response code. You can put this authorization engine behind API gateways, and reverse proxies to protect your APIs and services and allow them to formulate an authorization request to CAS, receive a response and translate that back to the caller.

In Norse mythology, Heimdall is a god and gatekeeper who keeps watch for invaders and is attested as possessing foreknowledge and keen senses. As gatekeeper, he is responsible for the rainbow bridge Bifrost and keeps a watchful eye on passengers.

The general flow can be summarized using the following steps:

  • Authorizable resources are registered with CAS
    • …with the appropriate method, URI, namespace and context
    • …with the appropriate authorization policies
  • Authorization request is submitted to CAS
    • …with the appropriate principal/subject
    • …with the appropriate method, URI, namespace and context
  • CAS locates the matching authorizable resource based on the request
  • …and then determines the principal/subject based on the request
  • CAS then consults the authorization engine to make a decision based on the resource, the principal and the request
  • CAS returns a response to the caller, either accepting or denying the request
:information_source: Usage

Note that CAS is simply acting as the policy definition point (PDP) as well as the policy information point (PIP). The authorization enforcement (PEP) must happen somewhere else by the calling party, which typically happens to be an API gateway or nginx reverse proxy, etc.

Configuration

Heimdall authorization support is enabled by including the following dependency in the overlay:

Show in CAS Initializr Generate CAS Server WAR Overlay 


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





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





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

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





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dependencies {
    /*
        The following platform references are included automatically and are listed for reference only.

        implementation enforcedPlatform("org.apereo.cas:cas-server-support-bom:${project.'cas.version'}")
        implementation platform(org.springframework.boot.gradle.plugin.SpringBootPlugin.BOM_COORDINATES)
        
    */
    implementation "org.apereo.cas:cas-server-support-heimdall"
}

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

cas.heimdall.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
SpringResourceProperties
cas.heimdall.jwt-assertion-max-lifetimeMaximum lifetime of a JWT bearer assertion presented to Heimdall, measured between its iat and exp claims.
PT5M
Duration

Maximum lifetime of a JWT bearer assertion presented to Heimdall, measured between its iat and exp claims. Such assertions must also carry a jti claim and are accepted only once.

Type
String
Default
PT5M
Defined by
HeimdallAuthorizationProperties

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.

:information_source: 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.

Topics

Actuator Endpoints

The following endpoints are provided by CAS:

heimdall
CAS endpoint5 operationsNot exposed by default
base path /cas/actuator/
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Turn the endpoint on and expose it over the web. One entry covers every operation. By default only info, health and status are exposed.



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management.endpoint.heimdall.access=UNRESTRICTED
management.endpoints.web.exposure.include=heimdall

Endpoints may be mapped to other paths. For example, to serve health at healthcheck:



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management.endpoints.web.path-mapping.health=healthcheck