A Shibboleth IdP v3.X plugin for authentication via an external CAS Server

This project was developed as part of Unicon's Open Source Support program. Professional support/integration assistance for this module is available. For more information, visit https://unicon.net/opensource/shibboleth.

This is a Shibboleth IDP external authentication plugin that delegates the authentication to an external Central Authentication Server. 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 consists of 2 components:

• A library (.jar) file that provides an IDP side servlet that acts as a bridge between CAS and the IDP
• Spring Webflow definition file (and bean definition file) that invokes the shib-cas-authn3 library.

Build Status

Software Requirements

This minimum supported version of Shibboleth Identity Provider is 3.3.0

A Shibboleth IdP v2.X plugin can be found at https://github.com/Unicon/shib-cas-authn2.

Installation

Overview

1. Copy the Spring Webflow files, jsp, and included jar files into the IDP_HOME.
2. Update the IdP's web.xml. (optional)
3. Update the IdP's idp.properties file.
4. Update the IdP's general-authn.xml file.
5. Rebuild the war file.

Copy the Spring Webflow files into the IDP_HOME

Copy the two xml files from the IDP_HOME directory (in the src tree) to the corresponding layout in your Shibboleth IdP home directory.

Update the IdP's web.xml (optional)

The servlet will register itself with the container when running under a Servlet 3.0 compliant container (such as Jetty 9). This step is provided for legacy reasons.

Add the ShibCas Auth Servlet entry in IDP_HOME/edit-webapp/WEB-INF/web.xml (Copy from IDP_HOME/webapp/WEB-INF/web.xml, if necessary.)

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/ExtCas/*</url-pattern>
    </servlet-mapping>
...

Update the IdP's idp.properties file

1. Set the idp.authn.flows to Shibcas. Or, for advance cases, add Shibcas to the list.
2. Add the additional properties.

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

# 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
...

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

Register the module with the IdP by adding the authn/Shibcas bean in IDP_HOME/conf/authn/general-authn.xml:

...
    <util:list id="shibboleth.AvailableAuthenticationFlows">

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

Rebuild the war file

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

CAS Service Registry

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.

Handling REFEDS MFA Profile

Note: This feature is only available, starting with version 3.2.4.

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)

Configuration

In the 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

You also need to ensure the authn/Shibcas flow is able to accept the requested principal in the IdP's general-authn.xml file, that is https://refeds.org/profile/mfa.

<bean id="authn/Shibcas" 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.