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A Shibboleth IdP v4.X plugin for delegating authentication to an external SSO Server using the CAS protocol

This is a Shibboleth IdP external authentication plugin that delegates primary authentication to an external Single Sign On Server using the Central Authentication Server protocol. The biggest advantage of using this component over the plain REMOTE_USER header solution provided by Shibboleth is the ability to utilize a full range of native CAS protocol features such as renew and gateway, plus the ability to share with CAS the EntityID of the relying application.

The plugin takes advantage of and extends the Shibboleth IdP's external authentication flow, and consists of a number of JAR artifacts that bridge the gap between Shibboleth and CAS.

Maintenance Status

Maintenance of this project is sponsored by Unicon's Open Source Support program. Professional support/integration assistance for this module is available. For more information, visit https://unicon.net/opensource/shibboleth.

Also, please do note that the Shibboleth IdP v3x+ has support for the CAS protocol and Apereo CAS server v5+ also has support for the SAML2 protocol. Unless justified otherwise, a better approach long-term would be to consolidate down to one platform removing the need to deploy and configure this plugin.

Software Requirements

This minimum supported version of Shibboleth Identity Provider is 4.3.0. See releases to find the the appropriate version.

Installation

Overview

• Download and extract the "latest release" zip or tar from releases.
• Copy the no-conversation-state.jsp file (also found inside this repo in IDP_HOME/edit-webapp) to your IdP's IDP_HOME/edit-webapp
• Copy two included jar files (cas-client-core-x.x.x.jar and shib-casuathenticator-x.x.x.jar) into the IDP_HOME/edit-webapp/WEB-INF/lib.
• Copy and Update the IdP's web.xml.
• Update the IdP's external-authn.xml file.
• (Optional) Update the IdP's general-authn.xml file.
• Update the IdP's idp.properties file.
• Rebuild the war file.

NOTE: You should ALWAYS refers to the README.md file that is packaged with the release for instructions.

Update the IdP's web.xml

Add the ShibCas Auth Servlet entry in IDP_HOME/edit-webapp/WEB-INF/web.xml. If there's no existing web.xml file in that location, copy the original from IDP_HOME/dist/webapp/WEB-INF/web.xml into IDP_HOME/edit-webapp/WEB-INF/web.xml and edit there.

Example snippet web.xml:

...
    <!-- Servlet for receiving a callback from an external CAS Server and continues the IdP login flow -->
    <servlet>
        <servlet-name>ShibCas Auth Servlet</servlet-name>
        <servlet-class>net.unicon.idp.externalauth.ShibcasAuthServlet</servlet-class>
        <load-on-startup>2</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>ShibCas Auth Servlet</servlet-name>
        <url-pattern>/Authn/External/*</url-pattern>
    </servlet-mapping>
...

Update the IdP's external-authn.xml file

In the IDP_HOME/authn/external-authn.xml file, ensure the context path points to Authn/External as shown below.

    <!-- Servlet context-relative path to wherever your implementation lives. -->
    <bean id="shibboleth.authn.External.externalAuthnPath" class="java.lang.String"
        c:_0="contextRelative:Authn/External" />

OPTIONAL Update the IdP's general-authn.xml file

You may also need to ensure the authn/External flow is able to accept passive and forced authentication if you wish to use those features. The authn/External bean is modified in the IDP_HOME/authn/general-authn.xml file as shown below. Note that non browser flow is not possible or supported so it should be false.

<bean id="authn/External" parent="shibboleth.AuthenticationFlow"
  p:passiveAuthenticationSupported="true"
  p:forcedAuthenticationSupported="true"
  p:nonBrowserSupported="false" />

Update the IdP's idp.properties file

1. Set the idp.authn.flows to External in IDP_HOME/conf/idp.properties. Or, for advance cases, add External to the list if you have others.
2. Add new properties for the ShibCas plugin.

...
# Regular expression matching login flows to enable, e.g. IPAddress|Password
#idp.authn.flows = Password
idp.authn.flows = External

# CAS Client properties (usage loosely matches that of the Java CAS Client)
## CAS Server Properties
shibcas.casServerUrlPrefix = https://cassserver.example.edu/cas
shibcas.casServerLoginUrl = ${shibcas.casServerUrlPrefix}/login

## Shibboleth Server Properties
shibcas.serverName = https://shibserver.example.edu

# By default you always get the AuthenticatedNameTranslator, add additional code to cover your custom needs.
# Takes a comma separated list of fully qualified class names
# shibcas.casToShibTranslators = com.your.institution.MyCustomNamedTranslatorClass
# shibcas.parameterBuilders = com.your.institution.MyParameterBuilderClass

# Specify CAS validator to use - either 'cas10', 'cas20' or 'cas30' (default)
# shibcas.ticketValidatorName = cas30


# Specify if the Relying Party/Service Provider entityId should be appended as a separate entityId query string parameter
# or embedded in the "service" querystring parameter - `append` (default) or `embed`
# shibcas.entityIdLocation = append
...

Rebuild the war file

From the IDP_HOME/bin directory, run ./build.sh or build.bat to rebuild the idp.war. Redeploy if necessary.

OPTIONAL EntityId / CAS Service Passing

By setting shibcas.entityIdLocation=embed, shib-cas-authn will embed the entityId in the service string so that CAS Server can use the entityId when evaluating a service registry entry match. Using serviceIds of something like: https://shibserver.example.edu/idp/Authn/ExtCas\?conversation=[a-z0-9]*&entityId=http://testsp.school.edu/sp or https://shibserver.example.edu/idp/Authn/ExtCas\?conversation=[a-z0-9]*&entityId=http://test.unicon.net/sp will match as two different entries in the service registry which will allow as CAS admin to enable MFA or use access strategies on an SP by SP basis.

OPTIONAL Handling REFEDS MFA Profile

The plugin has native support for REFEDS MFA profile. The requested authentication context class that is https://refeds.org/profile/mfa is passed along from the Shibboleth IdP over to this plugin and is then translated to a multifactor authentication strategy supported by and configured CAS (i.e. Duo Security). The CAS server is notified of the required authentication method via a special authn_method parameter by default. Once a service ticket is issued and plugin begins to validate the service ticket, it will attempt to ensure that the CAS-produced validation payload contains and can successfully assert the required/requested authentication context class.

The supported multifactor authentication providers are listed below:

• Duo Security (Requesting authn_method=mfa-duo and expecting validation payload attribute authnContextClass=mfa-duo)

REFEDS MFA Profile Configuration

In the IDP_HOME/conf/idp.properties file, ensure the following settings are set:

shibcas.casToShibTranslators = net.unicon.idp.externalauth.CasDuoSecurityRefedsAuthnMethodTranslator
shibcas.parameterBuilders = net.unicon.idp.authn.provider.extra.CasMultifactorRefedsToDuoSecurityAuthnMethodParameterBuilder

Finally add the authn context refs in the supported principals property list to authn/External in general-authn.xml as shown below.

<bean id="authn/External" parent="shibboleth.AuthenticationFlow"
  p:passiveAuthenticationSupported="true"
  p:forcedAuthenticationSupported="true"
  p:nonBrowserSupported="false">
    <property name="supportedPrincipals">
        <list>
            <bean parent="shibboleth.SAML2AuthnContextClassRef"
                  c:classRef="https://refeds.org/profile/mfa" />
              <bean parent="shibboleth.SAML2AuthnContextClassRef"
                  c:classRef="urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport" />
        </list>
    </property>
</bean>

Release Notes

See here.

Developer Notes

The project distributables can be built using ./gradlew clean build. The artifacts will be in build/distributions.

This project includes a Docker environment to assist with development/testing.

To build and execute: ./gradlew clean; ./gradlew up Then browse to: https://idptestbed/idp/profile/SAML2/Unsolicited/SSO?providerId=https://sp.idptestbed/shibboleth

You'll need a hosts file entry that points idptestbed to your Docker server's IP address.

The IdP only has a session of 1 minute (to test expired session/conversation key issues), so login into CAS Server quickly.