WORKERS AHEAD!

You are viewing the development documentation for the Apereo CAS server. The functionality presented here is not officially released yet. This is a work in progress and will be continually updated as development moves forward. You are most encouraged to test the changes presented.

JWT Secured Authorization Response Mode (JARM) - OpenID Connect Authentication

JWT Secured Authorization Response (JARM) allows for a number of strategies that allow a new JWT-based mode to encode authorization responses back to the client. This mechanism enhances the security of the standard authorization response with support for signing and optional encryption of the response. A signed response provides message integrity, sender authentication, audience restriction, and protection from mix-up attacks. Encrypting the response provides confidentiality of the response parameter values.

A relying party definition in CAS can be marked to produce JWT authorization responses:

{
  "@class": "org.apereo.cas.services.OidcRegisteredService",
  "clientId": "client",
  "serviceId": "https://app.example.org/redirect",
  "name": "Sample",
  "id": 1,
  "scopes" : [ "java.util.HashSet", [ "profile", "openid" ] ],
  "supportedResponseTypes": [ "java.util.HashSet", [ "code" ] ],
  "responseMode": "query.jwt"
}

JWT authorization responses produced by CAS can be signed and/or encrypted. The signing and encryption strategy should quite similar to that of ID tokens or access tokens.

The following example shows the JWT claims for a successful code authorization response:

{
    "iss": "https://sso.example.com/cas/oidc",
    "aud": "client",
    "exp": 1311281970,
    "code": "OC-1-...",
    "state": "..."
}

The response mode query.jwt causes CAS to send the authorization response as HTTP redirect to the redirect URI of the client. CAS adds the parameter response containing the JWT to the query component of the redirect URI:

HTTP/1.1 302 Found
Location: https://app.example.org/redirect?response=eyJraWQiOiJsYWViIiwiYWxnIjoiRVMyN...

The response mode fragment.jwt causes CAS to send the authorization response as HTTP redirect to the redirect URI of the client. The authorization server adds the parameter response containing the JWT to the fragment component of the redirect URI:

HTTP/1.1 302 Found
Location: https://app.example.org/redirect#response=eyJraWQiOiJsYWViIiwiYWxnIjoiRVMyN...

The response mode form_post.jwt causes CAS to POST the authorization response to the redirect URI of the client. The response parameter containing the JWT is encoded as HTML form value that is auto-submitted and thus is transmitted via the HTTP POST method to the client, with the result parameters being encoded in the body using the application/x-www-form-urlencoded format.

Configuration

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. In other words, you should only include this field in your
configuration if you need to modify the default value or if you need to turn on the feature controlled by the setting.}

cas.authn.oidc.jarm.expiration=PT60S

Hard timeout to kill the JWT token and expire it.

This settings supports the java.time.Duration syntax ^[?].

org.apereo.cas.configuration.model.support.oidc.OidcJwtAuthorizationResponseModeProperties.

_{How can I configure this property?}

Configuration properties can be included and activated using the following strategies.

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.

CAS properties can be specified using the Java configuration property syntax in any and all .properties files:

cas.authn.oidc.jarm.expiration=PT60S

This is the most common form of property configuration that is recognized by CAS, regardless of the actual property source, which might in fact be managed separately outside the CAS environment, by another system or cloud framework.

CAS properties can be specified using the YAML syntax:

cas: 
  authn: 
    oidc: 
      jarm: 
        expiration: "PT60S"

Note that YAML is very specific about structure and indentation. Be sure to verify the correctness of the final result with your YAML validator of choice.

CAS properties can be passed to the CAS web application as system properties, when the application is launched:

java -Dcas.authn.oidc.jarm.expiration="PT60S" -jar build/libs/cas.war

The above example assumes that the CAS web application is packaged as cas.war with an embedded server container and can be found in the build/libs directory. Note the placement of the system property which must be specified before the CAS web application is launched.

CAS properties can specified as system environment variables before the CAS web application is launched:

export CAS_AUTHN_OIDC_JARM_EXPIRATION="PT60S"

java -jar build/libs/cas.war

The above example assumes that the CAS web application is packaged as cas.war with an embedded server container and can be found in the build/libs directory.

CAS properties can be passed to the CAS web application as command-line arguments, when the application is launched:

java -jar build/libs/cas.war --cas.authn.oidc.jarm.expiration="PT60S"

The above example assumes that the CAS web application is packaged as cas.war with an embedded server container and can be found in the build/libs directory.

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

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, specially 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.