mod_auth_cas and AuthAuthoritative

[Volker Krebs]

Hello,
has anybody configured Apache to use mod_auth_cas as a fall back 
authentication service using the AuthAuthoritative Directive ?

I want to use mod_auth_dbm and if authentication fails, fall back to 
mod_auth_cas. But I doubt that it is even possible, since mod_auth_cas 
is not AuthType Basic or Digest.

The only thing I can think of, is something like mod_auth_cas forwards 
to mod_auth_dbm if no ticket is present.

Any Ideas ?

Thanks
Volker