[go-nuts] delegate to default mux for auth users

I found a comment on this mailing list that said it's possible to use a
custom mux for http.listening and have that mux delegate to the default mux
for authorized users, however, there's no code samples.

Can someone show

a) where check for authorized users would take place
b) how to default to default mux in case of authorized users and, if not
authorized, continue with custom mux

Thank you