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.
Authy Authenticator mfa-authy See this guide.
Acceptto mfa-acceptto See this guide.
YubiKey mfa-yubikey See this guide.
RSA/RADIUS mfa-radius See this guide.
WiKID mfa-radius See this guide.
Google Authenticator mfa-gauth See this guide.
FIDO U2F mfa-u2f See this guide.
FIDO2 WebAuthN mfa-webauthn See this guide.
CAS Simple mfa-simple See this guide.
Swivel Secure mfa-swivel See this guide.
Inwebo mfa-inwebo See this guide.
Custom Custom See this guide.
Azure Multifactor

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.

Core 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.

  • cas.authn.mfa.core.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 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.


    How can I configure this property?

    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. You should only include this field in your configuration if you need to modify the default value.

  • 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.

    How can I configure this property?

  • 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.

    How can I configure this property?

  • 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:

    • 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.

    How can I configure this property?

  • cas.authn.mfa.core.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.

    How can I configure this property?