Multifactor Authentication (MFA)
CAS provides support for a variety of multifactor authentication providers and options, while allowing one to design their own. The secondary authentication factor always kicks in after the primary step and existing authentication sessions will be asked to step-up to the needed multifactor authentication factor, should the request or trigger require it. The satisfied authentication context is communicated back to the application as well to denote a successful multifactor authentication event.
At a minimum, you need answer the following questions:
- Which provider(s) are we using for multifactor authentication?
- How and for whom are we triggering multifactor authentication?
Supported Providers
The following multifactor providers are supported by CAS.
Provider | Id | Instructions |
---|---|---|
Duo Security | mfa-duo |
See this guide. |
YubiKey | mfa-yubikey |
See this guide. |
RSA/RADIUS | mfa-radius |
See this guide. |
Google Authenticator | mfa-gauth |
See this guide. |
FIDO2 WebAuthN | mfa-webauthn |
See this guide. |
CAS Simple | mfa-simple |
See this guide. |
Inwebo | mfa-inwebo |
See this guide. |
Custom | Custom | See this guide. |
Microsoft has removed the ability for external SSO servers to use Azure MFA. To use Azure MFA, you must also have all your users authenticate using Azure AD SSO. You may want to route authentication requests to Azure AD SSO using the delegated authentication features of CAS.
Configuration
The following settings and properties are available from the CAS configuration catalog:
cas.authn.mfa.core.provider-selection.cookie.crypto.encryption.key=
The encryption key is a JWT whose length is defined by the encryption key size setting. This setting supports the Spring Expression Language.
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cas.authn.mfa.core.provider-selection.cookie.crypto.signing.key=
The signing key is a JWT whose length is defined by the signing key size setting. This setting supports the Spring Expression Language.
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cas.authn.mfa.core.provider-selection.provider-selector-groovy-script.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.authn.mfa.core.authentication-context-attribute=authnContextClass
Attribute returned in the final CAS validation payload that indicates the authentication context class satisfied in the event of a multifactor authentication attempt.
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cas.authn.mfa.core.content-type=application/cas
Content-type that is expected to be specified by non-web clients such as curl, etc in the event that the provider supports variations of non-browser based MFA. The value is treated as a regular expression. This settings supports regular expression patterns. [?].
|
cas.authn.mfa.core.global-failure-mode=
Defines the global failure mode for the entire deployment. This is meant to be used a shortcut to define the policy globally rather than per application. Applications registered with CAS can still define a failure mode and override the global. Available values are as follows:
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cas.authn.mfa.core.provider-selection.cookie.allowed-ip-addresses-pattern=
A regular expression pattern that indicates the set of allowed IP addresses, when This settings supports regular expression patterns. [?].
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cas.authn.mfa.core.provider-selection.cookie.auto-configure-cookie-path=true
Decide if cookie paths should be automatically configured based on the application context path, when the cookie path is not configured.
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cas.authn.mfa.core.provider-selection.cookie.domain=
Cookie domain. Specifies the domain within which this cookie should be presented. The form of the domain name is specified by RFC 2965. A domain name begins with a dot (.foo.com) and means that the cookie is visible to servers in a specified Domain Name System (DNS) zone (for example, www.foo.com, but not a.b.foo.com). By default, cookies are only returned to the server that sent them.
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cas.authn.mfa.core.provider-selection.cookie.enabled=true
Whether MFA selection should be remembered with cookies.
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cas.authn.mfa.core.provider-selection.cookie.geo-locate-client-session=false
When set to
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cas.authn.mfa.core.provider-selection.cookie.http-only=true
true if this cookie contains the HttpOnly attribute. This means that the cookie should not be accessible to scripting engines, like javascript.
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cas.authn.mfa.core.provider-selection.cookie.max-age=-1
The maximum age of the cookie, specified in seconds. By default,
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cas.authn.mfa.core.provider-selection.cookie.name=
Cookie name. Constructs a cookie with a specified name and value. The name must conform to RFC 2965. That means it can contain only ASCII alphanumeric characters and cannot contain commas, semicolons, or white space or begin with a
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cas.authn.mfa.core.provider-selection.cookie.path=
Cookie path. Specifies a path for the cookie to which the client should return the cookie. The cookie is visible to all the pages in the directory you specify, and all the pages in that directory's subdirectories. A cookie's path must include the servlet that set the cookie, for example, /catalog, which makes the cookie visible to all directories on the server under /catalog. Consult RFC 2965 (available on the Internet) for more information on setting path names for cookies.
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cas.authn.mfa.core.provider-selection.cookie.pin-to-session=true
When generating cookie values, determine whether the value should be compounded and signed with the properties of the current session, such as IP address, user-agent, etc.
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cas.authn.mfa.core.provider-selection.cookie.same-site-policy=
If a cookie is only intended to be accessed in a first party context, the developer has the option to apply one of settings SameSite=None , to designate cookies for cross-site access. When the SameSite=None attribute is present, an additional Secure attribute is used so cross-site cookies can only be accessed over HTTPS connections. Accepted values are:
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cas.authn.mfa.core.provider-selection.cookie.secure=true
True if sending this cookie should be restricted to a secure protocol, or false if the it can be sent using any protocol.
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cas.authn.mfa.core.provider-selection.provider-selection-enabled=false
In the event that multiple multifactor authentication providers are determined for a multifactor authentication transaction, this setting will allow one to interactively choose a provider out of the list of available providers. A trigger may be designed to support more than one provider, and rather than letting CAS auto-determine the selected provider via scripts or ranking strategies, this method puts the choice back onto the user to decide which provider makes the most sense at any given time.
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cas.authn.mfa.core.provider-selection.cookie.crypto.alg=
The signing/encryption algorithm to use.
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cas.authn.mfa.core.provider-selection.cookie.crypto.enabled=true
Whether crypto operations are enabled.
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cas.authn.mfa.core.provider-selection.cookie.crypto.encryption.key-size=512
The encryption key size.
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cas.authn.mfa.core.provider-selection.cookie.crypto.signing.key-size=512
The signing key size.
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cas.authn.mfa.core.provider-selection.cookie.crypto.strategy-type=ENCRYPT_AND_SIGN
Control the cipher sequence of operations. The accepted values are:
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cas.authn.mfa.core.provider-selection.cookie.crypto.encryption.key=
The encryption key is a JWT whose length is defined by the encryption key size setting. This setting supports the Spring Expression Language.
|
cas.authn.mfa.core.provider-selection.cookie.crypto.signing.key=
The signing key is a JWT whose length is defined by the signing key size setting. This setting supports the Spring Expression Language.
|
cas.authn.mfa.core.provider-selection.cookie.crypto.alg=
The signing/encryption algorithm to use.
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cas.authn.mfa.core.provider-selection.cookie.crypto.enabled=true
Whether crypto operations are enabled.
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cas.authn.mfa.core.provider-selection.cookie.crypto.encryption.key-size=512
The encryption key size.
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cas.authn.mfa.core.provider-selection.cookie.crypto.signing.key-size=512
The signing key size.
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cas.authn.mfa.core.provider-selection.cookie.crypto.strategy-type=ENCRYPT_AND_SIGN
Control the cipher sequence of operations. The accepted values are:
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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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5
{
"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.
Please review this guide to configure your build.
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
.
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.
Triggers
Multifactor authentication can be activated via a number of triggers. To learn more, please see this guide.
Bypass Rules
Each multifactor provider is equipped with options to allow for MFA bypass. To learn more, please see this guide.
Failure Modes
CAS will consult the current configuration in the event that the provider being requested is unreachable to determine how to proceed. To learn more, please see this guide.
Provider Selection
There are options and controls available to allow CAS to select a multifactor authentication provider, in case multiple triggers and conditions activate multiple providers. To learn more, please see this guide.