JWT Authentication

JSON Web Tokens are an open, industry standard RFC 7519 method for representing claims securely between two parties. CAS provides support for token-based authentication on top of JWT, where an authentication request can be granted an SSO session based on a form of credentials that are JWTs.

JWT Service Tickets

CAS may also be allowed to fully create signed/encrypted JWTs and pass them back to the application in form of service tickets. In this case, JWTs are entirely self-contained and contain the authenticated principal as well as all authorized attributes in form of JWT claims. To learn more about this functionality, please review this guide.

Overview

CAS expects a token parameter (or request header) to be passed along to the /login endpoint. The parameter value must be a JWT.

JCE Requirement

It's safe to make sure you have the proper JCE bundle installed in your Java environment that is used by CAS, specially if you need to use specific signing/encryption algorithms and methods. Be sure to pick the right version of the JCE for your Java version. Java versions can be detected via the java -version command.

Here is an example of how to generate a JWT via Pac4j:

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final String signingSecret = RandomUtils.randomAlphanumeric(256);
final String encryptionSecret = RandomUtils.randomAlphanumeric(48);

System.out.println("signingSecret " + signingSecret);
System.out.println("encryptionSecret " + encryptionSecret);

final JwtGenerator<CommonProfile> g = new JwtGenerator<>();
g.setSignatureConfiguration(new SecretSignatureConfiguration(signingSecret, JWSAlgorithm.HS256));
g.setEncryptionConfiguration(new SecretEncryptionConfiguration(encryptionSecret,
        JWEAlgorithm.DIR, EncryptionMethod.A192CBC_HS384));

final CommonProfile profile = new CommonProfile();
profile.setId("casuser");
final String token = g.generate(profile);
System.out.println("token: " + token);

Once the token is generated, you may pass it to the /login endpoint of CAS as such:

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/cas/login?service=https://...&token=<TOKEN_VALUE>

The token parameter may also be passed as a request header.

Configuration

JWT authentication support is enabled by including the following dependency in the WAR overlay:

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

dependencies {  
  implementation "org.apereo.cas:cas-server-support-token-webflow"
}

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.

  • cas.authn.token.principal-transformation.groovy.location=
  • The location of the resource. Resources can be URLS, or files found either on the classpath or outside somewhere in the file system.

  • cas.authn.token.crypto.encryption.key=
  • The encryption key is a JWT whose length is defined by the encryption key size setting.

  • cas.authn.token.crypto.signing.key=
  • The signing key is a JWT whose length is defined by the signing key size setting.

    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.authn.token.webflow.enabled=true
  • Whether webflow auto-configuration should be enabled.

  • cas.authn.token.webflow.order=0
  • The order in which the webflow is configured.

  • cas.authn.token.name=
  • Name of the authentication handler.

  • cas.authn.token.principal-transformation.blocking-pattern=
  • A regular expression that will be used against the username to match for blocking/forbidden values. If a match is found, an exception will be thrown and principal transformation will fail.

  • cas.authn.token.principal-transformation.case-conversion=
  • Indicate whether the principal identifier should be transformed into upper-case, lower-case, etc. Available values are as follows:

    • NONE: No conversion.
    • LOWERCASE: Lowercase conversion.
    • UPPERCASE: Uppercase conversion.

  • cas.authn.token.principal-transformation.pattern=
  • A regular expression that will be used against the provided username for username extractions. On a successful match, the first matched group in the pattern will be used as the extracted username.

  • cas.authn.token.principal-transformation.prefix=
  • Prefix to add to the principal id prior to authentication.

  • cas.authn.token.principal-transformation.suffix=
  • Suffix to add to the principal id prior to authentication.

  • cas.authn.token.crypto.alg=
  • The signing/encryption algorithm to use.

  • cas.authn.token.crypto.enabled=true
  • Whether crypto operations are enabled.

  • cas.authn.token.crypto.encryption-enabled=true
  • Whether crypto encryption operations are enabled.

  • cas.authn.token.crypto.encryption.key-size=512
  • The encryption key size.

  • cas.authn.token.crypto.signing-enabled=true
  • Whether crypto signing operations are enabled.

  • cas.authn.token.crypto.signing.key-size=512
  • The signing key size.

  • cas.authn.token.crypto.strategy-type=ENCRYPT_AND_SIGN
  • Control the cipher sequence of operations. The accepted values are:

    • ENCRYPT_AND_SIGN: Encrypt the value first, and then sign.
    • SIGN_AND_ENCRYPT: Sign the value first, and then encrypt.

    This CAS feature is able to accept signing and encryption crypto keys. In most scenarios if keys are not provided, CAS will auto-generate them. The following instructions apply if you wish to manually and beforehand create the signing and encryption keys.

    Note that if you are asked to create a JWK of a certain size for the key, you are to use the following set of commands to generate the token:

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    wget https://raw.githubusercontent.com/apereo/cas/master/etc/jwk-gen.jar
    java -jar jwk-gen.jar -t oct -s [size]
    

    The outcome would be similar to:

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    {
      "kty": "oct",
      "kid": "...",
      "k": "..."
    }
    

    The generated value for k needs to be assigned to the relevant CAS settings. Note that keys generated via the above algorithm are processed by CAS using the Advanced Encryption Standard (AES) algorithm which is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology.


    Authentication handlers as part of principal transformation may also be provided a path to a Groovy script to transform the provided username. The outline of the script may take on the following form:

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    def String run(final Object... args) {
        def providedUsername = args[0]
        def logger = args[1]
        return providedUsername.concat("SomethingElse")
    }
    

    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 below 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.

    Configure the appropriate service in your service registry to hold the secrets:

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    {
      "@class" : "org.apereo.cas.services.RegexRegisteredService",
      "serviceId" : "https://.+",
      "name" : "testId",
      "id" : 1,
      "properties" : {
        "@class" : "java.util.HashMap",
        "jwtSigningSecret" : {
          "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
          "values" : [ "java.util.HashSet", [ "<SECRET>" ] ]
        },
        "jwtEncryptionSecret" : {
          "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
          "values" : [ "java.util.HashSet", [ "<SECRET>" ] ]
        },
        "jwtSigningSecretAlg" : {
          "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
          "values" : [ "java.util.HashSet", [ "HS256" ] ]
        },
        "jwtEncryptionSecretAlg" : {
          "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
          "values" : [ "java.util.HashSet", [ "dir" ] ]
        },
        "jwtEncryptionSecretMethod" : {
          "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
          "values" : [ "java.util.HashSet", [ "A192CBC-HS384" ] ]
        },
        "jwtSecretsAreBase64Encoded" : {
           "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
           "values" : [ "java.util.HashSet", [ "false" ] ]
        }
      }
    }
    

    Note that the only required property is jwtSigningSecret.