CAS 6.5 w/ Duo MFA, was MFA actually used?

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Baron Fujimoto

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Jul 29, 2022, 3:45:20 PMJul 29
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We're currently using CAS 6.5 with Duo for MFA. While the MFA itself works, we're trying to find some way of determining whether MFA was actually used during a user's authentication.

MFA is not mandatory for our users, and they must opt-in and enroll themselves with Duo. We can see that when a user authenticates, there is a set of promising CAS authentication attributes available. e.g.:
- successfulAuthenticationHandlers: [DuoSecurityAuthenticationHandler]
- credentialType: [DuoSecurityCredential]
- authenticationMethod: [DuoSecurityAuthenticationHandler]
- authnContextClass: [mfa-duo]

However, these attributes appear to be assigned the same values whether the user is enrolled in Duo or not – and thus are presented with the MFA requirement during their login. Therefore, there doesn't appear to be anything in these attributes that allows us to distinguish whether MFA was actually invoked/required/used for the user's authentication.

FWIW, this is how we're currently enabling MFA for CAS in cas.properties:
cas.authn.mfa.triggers.global.global-provider-id=mfa-duo

We've looked at the available multifactor authentication triggers, but none of the attribute-based triggers seem appropriate since I think they rely on local information about the principal, and not something authoritative from Duo or about the actual CAS authentication flow that was used. Perhaps there's a way using the REST method with the Duo Auth API /enroll_status or /preauth endpoints, but that sounds kind of fraught (even if possible).

Is there something else we may be overlooking that would help us achieve our goal?
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Richard Frovarp

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Jul 29, 2022, 4:46:52 PMJul 29
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How are you triggering MFA / Duo? You likely only want to trigger Duo on a local attribute and setup the integration to force Duo always. If you are leaving it up to Duo to decide if the user is enrolled and bypass if not, the old Duo Web integration couldn't tell you what happen, just that they got past Duo. 6.5 should be using the new OIDC method, and it was supposed to return back more detail so you could make security decisions. So something there isn't working?? Here's my writeup about the Duo Web integration problems: https://www.frovarp.dev/2019/03/24/ambiguous-response-in-duo-web/

But in any event, I'd stick them in a group if they have to MFA and trigger Duo off of membership in that group, always enforcing MFA to happen on that integration.
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Mike Osterman

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Jul 29, 2022, 5:50:08 PMJul 29
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We are also non-mandatory MFA at present, and doing what Richard suggests. If they are a memberOf the AD group in question, they are required to Duo, regardless of service. 

# Active Directory LDAP connection
cas.authn.attributeRepository.ldap[0].attributes.memberOf=mfaAttribute

cas.authn.mfa.globalPrincipalAttributeNameTriggers=mfaAttribute
# MFA Group
cas.authn.mfa.globalPrincipalAttributeValueRegex=CN=MFA,OU=Something,DC=school,DC=edu

On a side note, we've talked about limiting some services to only users that are MFA'd (Apparently Transact will require if we want to use their Mobile Credential smart phone NFC functionality) and are looking towards service access strategies via the same group membership attribute:

Ray Bon

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Jul 29, 2022, 6:31:26 PMJul 29
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Baron,

We have been setting mfa in the service definition; some services are mandatory, others optional. Users can opt to enrol in duo in another internal application (where they can update other personal data, etc).

I have experimented with (but not used in prod):

# Specify the regular expression pattern to trigger multifactor when working with a single provider.
# Comment out the setting when working with multiple multifactor providers
# cas.authn.mfa.global-principal-attribute-value-regex=urn:mace:uvic.ca:university:duo_user

# Activate MFA globally based on authentication metadata attributes
# cas.authn.mfa.global-authentication-attribute-name-triggers=eduPersonEntitlement
# cas.authn.mfa.global-authentication-attribute-value-regex=urn:mace:uvic.ca:university:duo_user

Using the older style duo mfa [from within cas],the attributes are as you listed. When our user does not go through mfa, these attributes are set as:

successfulAuthenticationHandlers:  [LdapAuthenticationHandler]
credentialType:  [UsernamePasswordCredential]
authenticationMethod:  [LdapAuthenticationHandler]
no authContextClass

With the newer universal prompt, these attributes exist:

duoAuthCtxTxId  176187f6-63c6-453f-9e1a-43b1b50dd961
duoAuthResultStatus  allow
duoAuthCtxApplicationName  Web SDK Universal prompt
duoAuthCtxReason  remembered_device  (user_approved  on first login)
authnContextClass  mfa-duo
duoAuthCtxAccessDeviceIp  xxx.xxx.xxx.xxx
duoAuthCtxResult  success
duoAud  DI...
duoAuthCtxAccessDeviceLocationCity  Victoria
duoAuthCtxFactor  remembered_device (duo_push on first login)
duoAuthCtxTimestamp  1659132374
duoAuthCtxAccessDeviceLocationState  British Columbia
bypassMultifactorAuthentication  false
successfulAuthenticationHandlers  DuoSecurityAuthenticationHandler
duoSub  rbon
duoAuthCtxAccessDeviceLocationCountry  Canada
duoAuthCtxUserKey  DU...
credentialType  DuoSecurityUniversalPromptCredential
authenticationMethod  DuoSecurityAuthenticationHandler
duoIat  1.659132375E9
domain  uvic.ca
duoPreferredUsername  rbon
duoExp  1659135974
duoAuthTime  1659132374
duoAuthCtxEventType  authentication
duoAuthResult  allow 

So lots to choose from.

Ray

On Fri, 2022-07-29 at 09:44 -1000, Baron Fujimoto wrote:
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Baron Fujimoto

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Jul 29, 2022, 9:32:56 PMJul 29
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Thank you for all the replies. I think we're still using the Duo integration method to integrate with CAS that was prevalent circa CAS 5.x (Duo SDK?). I think at the time we finally upgraded to CAS 6.x, the Duo universal prompt stuff was still documented as not quite fully baked and "coming soon", so we deferred implementing that and stuck with what appeared to be successfully backwards compatible. It seems like with the newer methods we'd have more information available.

Because our MFA is opt-in, we've enabled it globally and not on a per-service basis. We've also currently leave the MFA requirements to the business logic in the applications themselves, but are trying to find ways to make that information for them more authoritative.

These replies give us options to investigate and consider for future deployments. Mahalo!

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