@dan, thanks for the directions.
It looks lik you have a way to make the SSO redirect work for their widget, but not for the portal version of their solution. The portal works with a "redirect" URL parameter that the authenticating party receives and needs to send back after authentication.
I don't think FA supports arbitrary URL parameter forwarding, so this is pretty much a no go directly out of the box.
I'll have a look at the widget, maybe that's a better solution for us anyway.