SAML2 Authentication

CAS can act as a SAML2 identity provider accepting authentication requests and producing SAML assertions.

If you intend to allow CAS to delegate authentication to an external SAML2 identity provider, you need to review this guide.

SAML Specification

This document solely focuses on what one might do to turn on SAML2 support inside CAS. It is not to describe/explain the numerous characteristics of the SAML2 protocol itself. If you are unsure about the concepts referred to on this page, please start with reviewing the SAML2 Specification.

Federation Interop Evaluation

The CAS project strives to conform to the SAML V2.0 Implementation Profile for Federation Interoperability. An evaluation of the requirements against the current CAS release is available here. It is recommended that you view, evaluate and comment on functionality that is currently either absent or marked questionable where verification is needed.

SAML Endpoints

The following CAS endpoints respond to supported SAML2 profiles:

/idp/profile/SAML2/Redirect/SSO
/idp/profile/SAML2/POST/SSO
/idp/profile/SAML2/POST-SimpleSign/SSO
/idp/profile/SAML2/POST/SLO
/idp/profile/SAML2/Redirect/SLO
/idp/profile/SAML2/Unsolicited/SSO
/idp/profile/SAML2/SOAP/ECP
/idp/profile/SAML2/SOAP/AttributeQuery
/idp/profile/SAML1/SOAP/ArtifactResolution

Metadata Management

Handling and storing SAML2 identity provider or service provider metadata can be done in a few ways. To learn more, please review this guide.

Configuration

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

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

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

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

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

You may also need to declare the following repository in your CAS overlay to be able to resolve dependencies:

repositories {
    maven { 
        mavenContent { releasesOnly() }
        url "https://build.shibboleth.net/nexus/content/repositories/releases" 
    }
}

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. You should only include this field in your
configuration if you need to modify the default value.}

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. 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, 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.

Actuator Endpoints

The following endpoints are provided by CAS:

SAML Services

Please see this guide to learn more about how to configure SAML2 service providers.

Security Configuration

Please see this guide to learn more about how to configure SAML2 security configuration.

Attribute Release

Attribute filtering and release policies are defined per SAML service. See this guide for more info.

Name ID Selection

Please see this guide to learn more about how to configure SAML2 security configuration.

Unsolicited SSO

SAML2 IdP Unsolicited/SSO profile supports the following parameters:

Parameter	Description
`providerId`	Required. Entity ID of the service provider.
`shire`	Optional. Response location (ACS URL) of the service provider.
`target`	Optional. Relay state.
`time`	Optional. Skew the authentication request.

Attribute Queries

In order to allow CAS to support and respond to attribute queries, you need to make sure the generated metadata has the AttributeAuthorityDescriptor element enabled, with protocol support enabled for urn:oasis:names:tc:SAML:2.0:protocol and relevant binding that corresponds to the CAS endpoint(s). You also must ensure the AttributeAuthorityDescriptor tag lists all KeyDescriptor elements and certificates that are used for signing as well as authentication, specially if the SOAP client of the service provider needs to cross-compare the certificate behind the CAS endpoint with what is defined for the AttributeAuthorityDescriptor. CAS by default will always use its own signing certificate for signing of the responses generated as a result of an attribute query.

Also note that support for attribute queries need to be explicitly enabled and the behavior is off by default, given it imposes a burden on CAS and the underlying ticket registry to keep track of attributes and responses as tickets and have them be later used and looked up.

Client Libraries

For Java-based applications, the following frameworks may be used to integrate your application with CAS acting as a SAML2 identity provider:

Sample Client Applications

Troubleshooting

To enable additional logging, modify the logging configuration file to add the following:

<Logger name="org.opensaml" level="debug" additivity="false">
    <AppenderRef ref="console"/>
    <AppenderRef ref="file"/>
</Logger>
<Logger name="PROTOCOL_MESSAGE" level="debug" additivity="false">
    <AppenderRef ref="console"/>
    <AppenderRef ref="file"/>
</Logger>