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. |
| Twilio | mfa-twilio |
See this guide. |
| Inwebo | mfa-inwebo |
See this guide. |
| Custom | Custom | See this guide. |
Comparison
| Provider | What the user does | External service | Registrations kept by CAS | Phishing-resistant |
|---|---|---|---|---|
| Duo Security | Approves a push, takes a call or enters a passcode | Duo | No, Duo keeps them | Depends on the Duo method |
| FIDO2 WebAuthn | Uses a passkey or security key | None | Yes | Yes |
| Google Authenticator | Enters a code from a TOTP app | None | Yes, in JSON, JPA, LDAP, MongoDb, Redis, DynamoDb or REST | No |
| YubiKey | Touches a YubiKey that types a one-time password | Yubico validation service | Yes, in JSON, JPA, MongoDb, Redis, DynamoDb or REST | No |
| RSA/RADIUS | Enters a code checked by a RADIUS server | Your RADIUS server, such as RSA | No | No |
| CAS Simple | Enters a code CAS sent by email, SMS or notification | An email or SMS provider | No, contact details come from user attributes | No |
| Twilio | Enters a code sent by SMS, WhatsApp or voice call | Twilio Verify | No, the recipient comes from a user attribute | No |
| Inwebo | Approves the login with Inwebo (TrustBuilder) | Inwebo | No, Inwebo keeps them | Depends on the Inwebo method |
Phishing-resistant factors are bound to the CAS site and cannot be replayed through a look-alike page. Codes and push approvals can be relayed by an attacker who controls such a page.
Microsoft Entra Multifactor Authentication
Microsoft has removed the ability for external SSO servers and identity providers to use Microsoft Entra multifactor authentication as a standalone MFA solution. To use Microsoft Entra multifactor authentication, you must also have all your users authenticate using Microsoft Entra ID SSO. You may want to route authentication requests to Microsoft Entra ID SSO using the delegated authentication features of CAS.
RememberSupport for Google Authenticator is not about supporting the mobile application itself. This is about supporting the TOTP algorithm that is used by the application to generate time-based one-time passwords. Any compliant mobile application that can generate TOTP codes can be used with CAS including LastPass, Microsoft Authenticator, Authy, etc.
Configuration
The following settings and properties are available from the CAS configuration catalog:
cas.authn.mfa.core.provider-selection.cookie.crypto.encryption.keyThe encryption key is a string whose length is defined by the encryption key size setting.
The encryption key is a string whose length is defined by the encryption key size setting.
cas.authn.mfa.core.provider-selection.cookie.crypto.signing.keyThe signing key is a string whose length is defined by the signing key size setting.
The signing key is a string whose length is defined by the signing key size setting.
cas.authn.mfa.core.provider-selection.provider-selector-groovy-script.locationThe location of the resource.
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, especially if the script is set to reload on changes, you may need to adjust the total number of inotify 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.
cas.authn.mfa.core.authentication-context-attributeAttribute returned in the final CAS validation payload that indicates the authentication context class satisfied in the event of a multifactor authentication attempt.
authnContextClassAttribute returned in the final CAS validation payload that indicates the authentication context class satisfied in the event of a multifactor authentication attempt.
cas.authn.mfa.core.content-typeContent-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.
application/casContent-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.
cas.authn.mfa.core.global-failure-modeDefines the global failure mode for the entire deployment.
closed-
OPEN: Disallow MFA, proceed with authentication but don't communicate MFA to the RP. -
CLOSED: Disallow MFA, block with authentication. -
PHANTOM: Disallow MFA, proceed with authentication and communicate MFA to the RP. -
NONE: Do not check for failure at all. -
UNDEFINED: The default one indicating that no failure mode is set at all.
cas.authn.mfa.core.provider-selection.cookie.allowed-ip-addresses-patternA regular expression pattern that indicates the set of allowed IP addresses, when #isPinToSession() is configured.
A regular expression pattern that indicates the set of allowed IP addresses, when #isPinToSession() is configured. In the event that there is a mismatch between the cookie IP address and the current request-provided IP address (i.e. network switches, VPN, etc), the cookie can still be considered valid if the new IP address matches the pattern specified here.
cas.authn.mfa.core.provider-selection.cookie.auto-configure-cookie-pathDecide if cookie paths should be automatically configured based on the application context path, when the cookie path is not configured.
trueDecide if cookie paths should be automatically configured based on the application context path, when the cookie path is not configured.
cas.authn.mfa.core.provider-selection.cookie.crypto.algThe signing/encryption algorithm to use.
The signing/encryption algorithm to use.
cas.authn.mfa.core.provider-selection.cookie.crypto.enabledWhether crypto operations are enabled.
trueWhether crypto operations are enabled.
cas.authn.mfa.core.provider-selection.cookie.crypto.encryption.key-sizeThe encryption key size.
512The encryption key size.
cas.authn.mfa.core.provider-selection.cookie.crypto.signing.key-sizeThe signing key size.
512The signing key size.
cas.authn.mfa.core.provider-selection.cookie.crypto.strategy-typeControl the cipher sequence of operations.
ENCRYPT_AND_SIGN-
ENCRYPT_AND_SIGN: Encrypt the value first, and then sign. -
SIGN_AND_ENCRYPT: Sign the value first, and then encrypt.
cas.authn.mfa.core.provider-selection.cookie.domainCookie 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.
cas.authn.mfa.core.provider-selection.cookie.enabledWhether MFA selection should be remembered with cookies.
trueWhether MFA selection should be remembered with cookies.
cas.authn.mfa.core.provider-selection.cookie.geo-locate-client-sessionWhen set to true and assuming #isPinToSession() is also true , client sessions (using the client IP address) are geo-located using a geolocation service when/if configured.
falseWhen set to true and assuming #isPinToSession() is also true, client sessions (using the client IP address) are geo-located using a geolocation service when/if configured. The resulting session is either pinned to the client geolocation, or the default client address.
cas.authn.mfa.core.provider-selection.cookie.http-onlytrue if this cookie contains the HttpOnly attribute.
truetrue if this cookie contains the HttpOnly attribute. This means that the cookie should not be accessible to scripting engines, like javascript.
cas.authn.mfa.core.provider-selection.cookie.max-ageThe maximum age of the cookie, specified in seconds.
-1The maximum age of the cookie, specified in seconds. By default, -1 indicating the cookie will persist until browser shutdown. A positive value indicates that the cookie will expire after that many seconds have passed. Note that the value is the maximum age when the cookie will expire, not the cookie's current age. A negative value means that the cookie is not stored persistently and will be deleted when the Web browser exits. A zero value causes the cookie to be deleted.
cas.authn.mfa.core.provider-selection.cookie.nameCookie 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 $ character. The cookie's name cannot be changed after creation. By default, cookies are created according to the RFC 2965 cookie specification. Cookie names are automatically calculated assigned by CAS at runtime, and there is usually no need to customize the name or assign it a different value unless a special use case warrants the change.
cas.authn.mfa.core.provider-selection.cookie.pathCookie 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.
cas.authn.mfa.core.provider-selection.cookie.pin-to-sessionWhen 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.
trueWhen 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.
Turning off session pinning is not exactly ideal. This is a barrier to prevent cookie replay attacks. A cookie that was created with an IP given a certain location cannot be replayed back in a different browser with a different IP from a different location.
There may however be legitimate reasons to turn it off and relax this after careful reviews, if you intend to support a type of user who intends to switch their IP quite frequently. A classic example is the type of user that is on VPN at the time of login, but decides to resume their work a few hours later off VPN or at a different location.
cas.authn.mfa.core.provider-selection.cookie.same-site-policyIf a cookie is only intended to be accessed in a first party context, the developer has the option to apply one of settings SameSite=Lax or SameSite=Strict or SameSite=None to prevent external access.
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=Lax or SameSite=Strict or SameSite=None to prevent external access.
To safeguard more websites and their users, the new secure-by-default model assumes all cookies should be protected from external access unless otherwise specified. Developers must use a new cookie setting, 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.
LaxStrictNone-
Off: Disable the generation of the SameSite cookie attribute altogether. - Path to a Groovy script that is able to generate the SameSite cookie attribute dynamically.
- Fully qualified name of a class that implements
org.apereo.cas.web.cookie.CookieSameSitePolicy
cas.authn.mfa.core.provider-selection.cookie.secureTrue if sending this cookie should be restricted to a secure protocol, or false if the it can be sent using any protocol.
trueTrue if sending this cookie should be restricted to a secure protocol, or false if the it can be sent using any protocol.
cas.authn.mfa.core.provider-selection.provider-selection-enabledIn 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...
falseIn 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.
cas.authn.mfa.core.provider-selection.provider-selection-optionalIf provider selection is enabled, this setting will allow the user to skip the provider selection step and proceed with authentication without having to select an MFA provider.
falseIf provider selection is enabled, this setting will allow the user to skip the provider selection step and proceed with authentication without having to select an MFA provider.
Required settings may be needed to activate or affect the feature; review them even when they have a default. Optional settings only need to be set to change a default or to turn on the behavior they control. Third party settings belong to libraries such as Spring Boot that CAS builds on; their own documentation may have more detail.
Signing & encryption
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:
1
2
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.
Groovy scripting
CAS takes advantage of Apache Groovy in forms of either embedded or external scripts that allow one to, by default, dynamically build constructs, attributes, access strategies and a lot more. To activate the functionality described here, you may need to prepare CAS to support and integrate with Apache Groovy.
Please review this guide to configure your build.
Notes on configuration
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, especially 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.