Principal Resolution
Principal resolution converts information in the authentication credential into a security principal that commonly contains additional attributes (i.e. user details such as affiliations, group membership, email, display name). A CAS principal contains a unique identifier by which the authenticated user will be known to all requesting services. A principal also contains optional attributes that may be released to services to support authorization and personalization. Principal resolution is a requisite part of the authentication process that happens after credential authentication.
The attribute retrieval and resolution process that is carried out by principal resolution is discussed here.
Configuration
CAS uses the Person Directory library to provide a flexible principal resolution services against a number of data
sources. The key to configuring PersonDirectoryPrincipalResolver is the definition of an PersonAttributeDao object.
The following settings and properties are available from the CAS configuration catalog:
cas.person-directory.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. In the event the configured resource is a Groovy script, specially if the script set to reload on changes, you may need to adjust the total number ofinotify instances. On Linux, you may need to add the following line to /etc/sysctl.conf: fs.inotify.max_user_instances = 256. You can check the current value via cat /proc/sys/fs/inotify/max_user_instances. In situations and scenarios where CAS is able to automatically watch the underlying resource for changes and detect updates and modifications dynamically, you may be able to specify the following setting as either an environment variable or system property with a value of false to disable the resource watcher: org.apereo.cas.util.io.PathWatcherService.
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cas.person-directory.active-attribute-repository-ids=*
Activated attribute repository identifiers that should be used for fetching attributes if attribute resolution is enabled. The list here may include identifiers separated by comma.
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cas.person-directory.attribute-repository-selection=
Control the behavior of the attribute repository selection by authentication method or handler. The map here is keyed by the authentication handler name, and the value is the attribute repository identifiers separated by comma. When the authentication handler is executed, the attribute repositories assigned to this handler will be selected to fetch attributes. Note that the resolution engine will always favor attribute repositories assigned to the service definition, if any and as part of its authentication policy, over this global setting.
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cas.person-directory.attribute-resolution-enabled=
Whether attribute repositories should be contacted to fetch person attributes. Defaults to true if not set. Available values are as follows:
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cas.person-directory.principal-attribute=
Attribute name to use to indicate the identifier of the principal constructed. If the attribute is blank or has no values, the default principal id will be used determined by the underlying authentication engine. The principal id attribute usually is removed from the collection of attributes collected, though this behavior depends on the schematics of the underlying authentication strategy.
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cas.person-directory.principal-resolution-conflict-strategy=last
In the event that the principal resolution engine resolves more than one principal, (specially if such principals in the chain have different identifiers), this setting determines strategy by which the principal id would be chosen from the chain. Accepted values are:
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cas.person-directory.principal-resolution-failure-fatal=
When true, throws an error back indicating that principal resolution has failed and no principal can be found based on the authentication requirements. Otherwise, logs the condition as an error without raising a catastrophic error. Available values are as follows:
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cas.person-directory.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. This setting supports the Spring Expression Language.
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cas.person-directory.principal-transformation.case-conversion=NONE
Indicate whether the principal identifier should be transformed into upper-case, lower-case, etc. Available values are as follows:
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cas.person-directory.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. This setting supports the Spring Expression Language.
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cas.person-directory.principal-transformation.prefix=
Prefix to add to the principal id prior to authentication. This setting supports the Spring Expression Language.
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cas.person-directory.principal-transformation.suffix=
Suffix to add to the principal id prior to authentication. This setting supports the Spring Expression Language.
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cas.person-directory.return-null=
Return a null principal object if no attributes can be found for the principal. Available values are as follows:
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cas.person-directory.use-existing-principal-id=
Uses an existing principal id that may have already been established in order to run person directory queries. This is generally useful in situations where authentication is delegated to an external identity provider and a principal is first established to then query an attribute source. Available values are as follows:
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Please review this guide to configure your build.
cas.person-directory.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. In the event the configured resource is a Groovy script, specially if the script set to reload on changes, you may need to adjust the total number ofinotify instances. On Linux, you may need to add the following line to /etc/sysctl.conf: fs.inotify.max_user_instances = 256. You can check the current value via cat /proc/sys/fs/inotify/max_user_instances. In situations and scenarios where CAS is able to automatically watch the underlying resource for changes and detect updates and modifications dynamically, you may be able to specify the following setting as either an environment variable or system property with a value of false to disable the resource watcher: org.apereo.cas.util.io.PathWatcherService.
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cas.person-directory.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. This setting supports the Spring Expression Language.
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cas.person-directory.principal-transformation.case-conversion=NONE
Indicate whether the principal identifier should be transformed into upper-case, lower-case, etc. Available values are as follows:
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cas.person-directory.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. This setting supports the Spring Expression Language.
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cas.person-directory.principal-transformation.prefix=
Prefix to add to the principal id prior to authentication. This setting supports the Spring Expression Language.
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cas.person-directory.principal-transformation.suffix=
Suffix to add to the principal id prior to authentication. This setting supports the Spring Expression Language.
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Authentication handlers that generally deal with username-password credentials can be configured to transform the user id prior to executing the authentication sequence. Each authentication strategy in CAS provides settings to properly transform the principal. Refer to the relevant settings for the authentication strategy at hand to learn more.
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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String run(final Object... args) {
def (providedUsername,logger) = args
return providedUsername.concat("SomethingElse")
}
To prepare CAS to support and integrate with Apache Groovy, please review this guide.
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.
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.
Custom
You may also design and register your own principal resolution strategy by supplying an implementation of
the PrincipalResolver component and registering it with the runtime context:
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@AutoConfiguration
public static class MyConfiguration {
@Bean
public PrincipalResolver myPrincipalResolver() {
return new MyPrincipalResolver();
}
@Bean
public PrincipalResolutionExecutionPlanConfigurer myExecutionPlanConfigurer(
@Qualifier("myPrincipalResolver")
final PrincipalResolver myPrincipalResolver) {
return plan -> {
plan.registerPrincipalResolver(myPrincipalResolver);
};
}
}
See this guide to learn more about how to register configurations into the CAS runtime.