How to determine how users log into CPQ

We have some users who come to CPQ from an external system and other users who log directly into CPQ. We need to change some CPQ behavior based on how those users entered CPQ (not necessarily whether they have an active session in the external system).

Specifically, we are trying to change the CPQ UI depending on whether a user logs in directly to CPQ or if the same user is directed to CPQ from our eCommerce portal. Ideally, we would be able to capture the origin uri if the user enters CPQ through a link/redirect. If this is not possible, it may suffice to detect whether the current session was started through username/password or through SAML SSO.