Overview

Google Apps for Education (or any of the Google Apps) utilizes SAML 2.0 to provide an integration point for external authentication services.

Usage

The Google Apps for Education integration described here allows CAS to act as a miniaturized SAML2 identity provider, for deployments that may not be prepared to turn on and allow CAS to fully act as a SAML2 identity provider. This feature is deprecated and is scheduled to be removed in the future. It does not make much sense to turn on and use both features in CAS at the same time, as one outranks the other and it is likely that using both features in CAS simultaneously would interfere with the functionality of both. If you can, consider using the SAML2 identity provider functionality in CAS to handle this integration as you would any other SAML2 service provider.

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

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<dependency>
  <groupId>org.apereo.cas</groupId>
  <artifactId>cas-server-support-saml-googleapps</artifactId>
  <version>${cas.version}</version>
</dependency>
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implementation "org.apereo.cas:cas-server-support-saml-googleapps:${project.'cas.version'}"
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dependencyManagement {
  imports {
    mavenBom "org.apereo.cas:cas-server-support-bom:${project.'cas.version'}"
  }
}

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

Generate Public/Private Keys

The first step is to generate DSA/RSA public and private keys. These are used to sign and read the Assertions. After keys are created, the public key needs to be registered with Google.

The keys will also need to be available to the CAS application (but not publicly available over the Internet) via the classpath though any location accessible by the user running the web server instance and not served publicly to the Internet is acceptable. Thus, inside src/main/resources is nice because it is scoped to the web application but not normally served. /etc/cas/ is also fine as well and protects the key from being overwritten on deploy of a new CAS webapp version.

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openssl genrsa -out private.key 1024
openssl rsa -pubout -in private.key -out public.key -inform PEM -outform DER
openssl pkcs8 -topk8 -inform PER -outform DER -nocrypt -in private.key -out private.p8
openssl req -new -x509 -key private.key -out x509.pem -days 365

The x509.pem file should be uploaded into Google Apps under Security/SSO.

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.

  • cas.google-apps.key-algorithm=RSA
  • Signature algorithm used to generate keys. Deprecation: Since 6.2

    org.apereo.cas.configuration.model.support.saml.googleapps.GoogleAppsProperties.

    Deprecation status is ERROR without a replacement setting.

    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.S ettings 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.