Surrogate Authentication

Surrogate authentication (impersonation), sometimes known as sudo for the web, is the ability to authenticate on behalf of another user.

The two actors in this case are:

  1. The primary admin user whose credentials are verified upon authentication.
  2. The surrogate user, selected by the admin, to which CAS will switch after credential verification and is one that is linked to the single sign-on session.

Example use cases for impersonation include:

  1. Logging into an application on behalf of a user to execute and make changes.
  2. Troubleshoot a bothersome authentication experience with an application on behalf of another user.

Surrogate authentication is enabled by including the following dependencies in the WAR overlay:



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<dependency>
    <groupId>org.apereo.cas</groupId>
    <artifactId>cas-server-support-surrogate-webflow</artifactId>
    <version>${cas.version}</version>
</dependency>





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implementation "org.apereo.cas:cas-server-support-surrogate-webflow:${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-surrogate-webflow"
}





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dependencies {
    /*
        The following platform references should be included automatically and are listed here for reference only.

        implementation enforcedPlatform("org.apereo.cas:cas-server-support-bom:${project.'cas.version'}")
        implementation platform(org.springframework.boot.gradle.plugin.SpringBootPlugin.BOM_COORDINATES)
        
    */
    implementation "org.apereo.cas:cas-server-support-surrogate-webflow"
}

Configuration

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. In other words, you should only include this field in your configuration if you need to modify the default value or if you need to turn on the feature controlled by the setting.

  • cas.authn.surrogate.core.principal-attribute-names=

    • Impersonation can be authorized for all primary users/subjects carrying specific attributes with a predefined matching value specified via #principalAttributeValues. Needless to say, the attributes need to have been resolved for the primary principal prior to this step. Matching and comparison operations are case insensitive.

    org.apereo.cas.configuration.model.support.surrogate.SurrogateCoreAuthenticationProperties.

    How can I configure this property?

  • cas.authn.surrogate.core.principal-attribute-values=

    • The regular expression that is cross matched against the principal attribute to determine if the account is authorized for impersonation. Matching and comparison operations are case insensitive.

    This settings supports regular expression patterns. [?].

    org.apereo.cas.configuration.model.support.surrogate.SurrogateCoreAuthenticationProperties.

    How can I configure this property?

  • cas.authn.surrogate.core.separator=+

    • The separator character used to distinguish between the surrogate account and the admin/primary account. For example, if you are casuser and you need to switch to jsmith as the surrogate (impersonated) user, the username provided to CAS would be jsmith+casuser.

    org.apereo.cas.configuration.model.support.surrogate.SurrogateCoreAuthenticationProperties.

    How can I configure this property?

    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.

    :information_source: Note

    When possible, properties should be stored in lower-case kebab format, such as cas.property-name=value. The only possible exception to this rule is when naming actuator endpoints; The name of the actuator endpoints (i.e. ssoSessions) MUST remain in camelCase mode.

    Settings 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. 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.

    Account Storage

    The following account stores may be configured and used to locate surrogates authorized for a particular user.

    Storage Description
    Simple See this guide.
    JSON See this guide.
    LDAP See this guide.
    JDBC See this guide.
    REST See this guide.
    Groovy See this guide.
    Custom See this guide.

    Note that multiple account stores may be combined and can function simultaneously together to locate accounts from different stores.

    Account Selection

    Please see this guide.

    Session Expiration

    Please see this guide.

    Surrogate Attributes

    Upon a successful surrogate authentication event, the following attributes are communicated back to the application in order to detect an impersonation session:

    Attribute Instructions
    surrogateEnabled Boolean to indicate whether session is impersonated.
    surrogatePrincipal The admin user whose credentials are validated and acts as the impersonator.
    surrogateUser The surrogate user that is impersonated.

    Surrogate Access Strategy

    Please see this guide.

    Surrogate Audits

    Please see this guide.

    Surrogate Principal Resolution

    Please see this guide.

    REST Protocol

    The feature extends the CAS REST API communication model to surrogate authentication, allowing REST credentials to specify a substitute and authenticate on behalf of another user. To activate surrogate authentication for the CAS REST API, you will need to choose one of the following options:

    • Format the credential username using the following syntax:
    

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    [surrogate-userid][separator][primary-userid]
    • Pass along a special request header X-Surrogate-Principal that contains the surrogate userid.