FIDO2 WebAuthn Multifactor Authentication - QR Codes

CAS can be configured to support FIDO2 WebAuthn authentication using QR codes. Once enabled, this feature allows users to authenticate using a FIDO2-enabled device by scanning a QR code presented by CAS. This authentication flow is mainly useful in scenarios where the primary authentication device (e.g. a laptop) is separate from the device that is used for FIDO2 authentication (e.g. a mobile phone). The flow follows these steps:

  • The user is prompted for their FIDO2-enabled device on their primary authentication device (i.e. laptop).
    • User decides here that FIDO2 authentication on the primary device is impossible or impractical.
  • CAS in parallel presents a QR code on the primary device that is then scanned by the user’s secondary FIDO2-enabled device (i.e. phone).
  • The scanned QR code contains a link that prompts the user to complete the FIDO authentication attempt with CAS.
    • This attempt is handled directly on the user’s secondary device, completely separate from the primary device.
  • Once the user has established a session on the secondary device, the primary authentication device is notified and will resume the flow.

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.web-authn.core.trust-source.trusted-device-metadata.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, 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.

    org.apereo.cas.configuration.model.SpringResourceProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.application-id=

    • The extension input to set for the appid extension when initiating authentication operations. If this member is set, starting an assertion op will automatically set the appid extension input, and finish assertion op will adjust its verification logic to also accept this AppID as an alternative to the RP ID. By default, this is not set.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.relying-party-id=

    • The id that will be set as the rp parameter when initiating registration operations, and which id hash will be compared against. This is a required parameter. A successful registration or authentication operation requires rp id hash to exactly equal the SHA-256 hash of this id member. Alternatively, it may instead equal the SHA-256 hash of application id if the latter is present.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.relying-party-name=

    • The human-palatable name of the Relaying Party.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.trust-source.fido.legal-header=

    • Set legal headers expected in the metadata BLOB. By using the FIDO Metadata Service, you will be subject to its terms of service. This setting serves two purposes:

    To remind you and any adopters/reviewers that you need to read those terms of service before using this feature. To help you detect if the legal header changes, so you can take appropriate action.

    If the legal header in the downloaded BLOB does not equal any of the expected headers, an exception will be thrown in the finalizing configuration step.

    Note that CAS makes no guarantee that a change to the FIDO Metadata Service terms of service will also cause a change to the legal header in the BLOB.

    The current legal header is noted by: #DEFAULT_LEGAL_HEADER which is the following:


    "Retrieval and use of this BLOB indicates acceptance of the appropriate agreement located at https://fidoalliance.org/metadata/metadata-legal-terms/".

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAttestationTrustSourceFidoProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.trust-source.fido.metadata-blob-url=https://mds.fidoalliance.org/

    • Download the metadata BLOB from the FIDO website. This is the current FIDO Metadata Service BLOB download URL.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAttestationTrustSourceFidoProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.trust-source.fido.trust-root-hash=cbb522d7b7f127ad6a0113865bdf1cd4102e7d0759af635a7cf4720dc963c53b

    • Certificate SHA-256 hash required for PKI to verify the downloaded certificate. Separate hash values with a comma.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAttestationTrustSourceFidoProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.trust-source.fido.trust-root-url=https://secure.globalsign.com/cacert/root-r3.crt

    • Certificate required for PKI to verify the downloaded blob. This is the current FIDO Metadata Service trust root certificate. If the cert is downloaded, it is also written to the cache File. The certificate will be downloaded if it does not exist in the cache, or if the cached certificate is not currently valid.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAttestationTrustSourceFidoProperties.

    Copy Configuration Property 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. 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.mfa.web-authn.core.allow-primary-authentication=false

    • Configure the authentication flow to allow web-authn to be used as the first primary factor for authentication. Registered accounts with a valid webauthn registration record can choose to login using their device as the first step.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.allow-untrusted-attestation=false

    • If false finish registration op will only allow registrations where the attestation signature can be linked to a trusted attestation root. This excludes self attestation and none attestation. Regardless of the value of this option, invalid attestation statements of supported formats will always be rejected. For example, a "packed" attestation statement with an invalid signature will be rejected even if this option is set to true.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.allowed-origins=

    • The allowed origins that returned authenticator responses will be compared against. The default is set to the server name. A successful registration or authentication operation requires origins to exactly equal one of these values.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.attestation-conveyance-preference=DIRECT

    • Accepted values are: DIRECT, INDIRECT, NONE. The argument for the attestation parameter in registration operations. Unless your application has a concrete policy for authenticator attestation, it is recommended to leave this parameter undefined.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.authenticator-attachment=

    • Specifies the desired authenticator attachment modality during credential registration.

    This is used by the WebAuthn client/browser to select which type of authenticator may be used to create the credential.

    • PLATFORM: an authenticator built into, or tightly bound to, the user's device, such as Touch ID, Windows Hello, Android/iOS passkeys.
    • CROSS_PLATFORM: an external/roaming authenticator usable across multiple devices, such as a USB, NFC, or BLE security key like a YubiKey.

    If unset, the client may use any available authenticator.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.display-name-attribute=displayName

    • Name of the principal attribute that indicates the principal's display name, primarily used for device registration.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.enabled=true

    • Whether WebAuthn functionality should be activated and enabled.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.expire-devices=30

    • Expire and forget device registration records after this period.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.expire-devices-time-unit=days

    • Device registration record expiration time unit.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.multiple-device-registration-enabled=false

    • When enabled, allows the user/system to accept multiple accounts and device registrations per user, allowing one to switch between or register new devices/accounts automatically.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.qr-code-authentication-enabled=false

    • When enabled, allows the user to a scan a QR code on an external device and authenticate later on the primary device. This is useful in scenarios where the primary authentication device is not registered with CAS and the user has a secondary device that is registered and does not wish to use the primary device to authenticate for security or other practical reasons.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.trust-source.fido.blob-cache-file=

    • Cache metadata BLOB in the file cache file. If cache file exists, is a normal file, is readable, and is not out of date, then it will be used as the FIDO Metadata Service BLOB.

    Otherwise, the metadata BLOB will be downloaded and written to this file.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAttestationTrustSourceFidoProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.trust-source.fido.trust-root-cache-file=

    • Cache the trust root certificate in the file cache file. If cache file exists, is a normal file, is readable, matches one of the SHA-256 hashes configured in and contains a currently valid X.509 certificate, then it will be used as the trust root for the FIDO Metadata Service blob.

    Otherwise, the trust root certificate will be downloaded and written to this file.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAttestationTrustSourceFidoProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.trusted-device-enabled=false

    • Indicates whether this provider should support trusted devices.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.user-verification-requirement=

    • Specifies the relying party's requirement for user verification during credential registration and/or authentication.

    User verification means the authenticator verifies the user locally, for example with a PIN, fingerprint, face recognition, or device unlock. This is stronger than simple user presence, such as touching a security key.

    • REQUIRED: user verification must be performed; the operation should fail if it is unavailable or not completed.
    • PREFERRED: user verification should be performed if possible, but the operation may still succeed without it.
    • DISCOURAGED: user verification is not requested, typically to reduce friction or avoid prompting for PIN/biometric verification.

    The server should validate the resulting authenticator data flags according to the configured requirement.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property How can I configure this property?

  • cas.authn.mfa.web-authn.core.validate-signature-counter=true

    • If true, finish assertion op will fail if the signature counter value in the response is not strictly greater than the stored signature counter value.

    org.apereo.cas.configuration.model.support.mfa.webauthn.WebAuthnMultifactorAuthenticationCoreProperties.

    Copy Configuration Property 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, 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.