Public workstation functionality doesn't work with Duo Universal Prompt

[Richard Frovarp]

I have two otherwise identically configured CAS configurations, both on
6.6.6. Both are configured to use Duo, and both of them have the public
workstation checkbox in the login form. The only difference between the
two is that one uses the iframe Duo integration and one uses the
Universal Prompt. The one using iframe will enforce the public
workstation checkbox when checked by asking for creds again on the
second service. The one using Universal Prompt won't. Best guess is
that this is a bug somewhere. I haven't had a chance to attempt to
track it down.

Richard