Carl, 

This is very helpful.  We actually run two CAS instances because of our IDP 
configuration.  One (the one in question here) requires MFA while the other 
does not.  So, if the CAS ticket in question is only valid in the MFA CAS 
instance, we can be certain the user has performed MFA.  In that case, it 
seems like the CAS ticket is enough, right?  Again, just checking my logic 
so sorry for redundant questions.  

-Matt

On Friday, September 7, 2018 at 9:55:48 AM UTC-5, waldbiec wrote:
>
> Matt, 
>
> It depends.  If during CAS ticket validation, the validation result can 
> assert that MFA took place for the authentication that created the TGT, 
> then I think that would be sufficient if your requirement is simply that 
> MFA took place already in the SSO session. 
>
> However, suppose not all services require MFA.  If you first establish an 
> SSO session to such a service, you might not be prompted for MFA.  When you 
> next go to a service that requires MFA, CAS would need to check in with the 
> IdP so it could perform MFA, or else the SSO session would be denied access 
> until it was terminated and a new SSO session was started that actually did 
> use MFA. 
>
> If your setup is such that in order to establish an SSO session, you need 
> to have provided a 2nd factor, then I would agree that CAS shouldn't need 
> to check with the IdP each time whether MFA is valid-- the fact that the 
> SSO session exists at all is based on the fact that MFA was successful. 
>  Whether it is possible to configure the software that way, I'm not sure. 
>
> Our own setup is the opposite of yours.  We run both CAS and Shibboleth 
> services.  CAS clients interface directly with our CAS service.  SAML2 
> clients interact with our Shibboleth IdP, but the IdP delegates all 
> authentication to CAS so the SSO experience is unified.  Our CAS service 
> does need to signal to the IdP if MFA was used to establish the session. 
>  We require MFA on a per-user basis.  Either a user will be required to use 
> MFA to establish an SSO session or it will not.  Any call to our IdP will 
> always pass though to CAS to verify an SSO session exists.  Users are only 
> prompted for MFA once per session. 
>
> Thanks, 
> Carl Waldbieser 
> ITS Identity Management 
> Lafayette College 
>
> ----- Original Message ----- 
> From: "Matt T" <j.matt....@gmail.com <javascript:>> 
> To: "cas-user" <cas-...@apereo.org <javascript:>> 
> Sent: Friday, 7 September, 2018 09:54:07 
> Subject: [cas-user] Should the CAS ticket be authoritative? 
>
> Hi Everyone, 
>
> I'll be the first to admin I'm no CAS expert.  In fact, I don't even 
> manage 
> our deployments here.  Instead, I work with applications which interface 
> with it so I do understand to some degree.  That being said, I have a 
> question which came up in internal discussions I'm hoping to get some 
> input 
> on. 
>
> We have CAS delegating authentication to our IDP.  Our IDP enforces 
> two-factor auth so if we require it, we don't have to facilitate with CAS. 
>   
> We've run into an issue where every request to an application behind 
> two-factor prompts the user for the second factor of authentication.  This 
> happens even when in a browser you've already verified.  This is an issue 
> because it takes away from the true SSO experience and a user can't move 
> from app to app. 
>
> The main reason it is asking for the second factor again is due to the way 
> we integrate CAS into our IDP.  That's a whole different topic and really 
> outside of the scope of this questions so just know we're aware of why it 
> happens even if it isn't right. 
>
> The question is this.  Is CAS ticket validity secure enough to trust only 
> that?  Why should we even check with our IDP a second time if the user's 
> session already has a valid CAS ticket?  Do others use this configuration 
> or do you always check with the IDP? 
>
> It seems like trusting the CAS ticket if valid is the best option and 
> would 
> allow us to better control application logins and state but maybe I'm not 
> thinking it all the way through. 
>
> Thanks in advance for any insight! 
>
> -Matt 
>
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