Google Apps (G Suite) can be configured to use CAS as a SAML2 IdP for single sign-on.

Google Apps (G Suite) allows an external SAML2 identity provider (IdP) to be used for user authentication (single sign-on) as an alternative to storing user passwords on Google’s servers. Support for Google’s specific SAML2 implementation was originally added to CAS in the CAS 3.x days, before CAS included general support for the SAML2 protocol. This code has been brought forward to CAS 5, and so integrating Google Apps is still done separately (and differently) from integrating other SAML2 services.

Add the Google Apps dependency to the project object model

To add Google Apps support to the CAS server, edit the pom.xml in the cas-overlay-template directory on the master build server (casdev-master) and locate the dependencies section (around line 69), which should look something like this:

<dependencies>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-webapp${app.server}</artifactId>
        <version>${cas.version}</version>
        <type>war</type>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-mongo-service-registry</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-ldap</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-saml</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-saml-idp</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-duo</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-mongo-ticket-registry</artifactId>
        <version>${cas.version}</version>
    </dependency>
</dependencies>

Insert a dependency for cas-server-support-saml-googleapps below the one for cas-server-support-saml-idp:

<dependencies>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-webapp${app.server}</artifactId>
        <version>${cas.version}</version>
        <type>war</type>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-mongo-service-registry</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-ldap</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-saml</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-saml-idp</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-saml-googleapps</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-duo</artifactId>
        <version>${cas.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apereo.cas</groupId>
        <artifactId>cas-server-support-mongo-ticket-registry</artifactId>
        <version>${cas.version}</version>
    </dependency>
</dependencies>

This will instruct Maven to download the appropriate code modules and build them into the server.

Rebuild the server

Run Maven to rebuild the server according to the new model:

casdev-master# ./mvnw clean package
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building cas-overlay 1.0
[INFO] ------------------------------------------------------------------------
(lots of diagnostic output... check for errors)
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 17.257 s
[INFO] Finished at: YYYY-MM-DDTHH:MM:SS-00:00
[INFO] Final Memory: 39M/97M
[INFO] ------------------------------------------------------------------------
casdev-master#

References