My friend Bruno does something for a captive portal that I thought might 
be interesting. Here's what he told me he does:

"I do captive portal by redirecting trafic to local port 80 and
using an modified http server (busybox http) to print a error
page (with a redirect) to any page not found locally

as the http server don't have any pages, all will be redirect
to my main server (access to it is granted through the portal)."

I asked him if I could share this with the m0n0wall list and he said:
" you can share my idea freely but I don't think it will be "the"
  solution for everyones cases... remember I force ppl to load
  PPTP on top of their systems, and my "captive portal" only tells
  the user to do so (for space constrainghts, redirecting to an
  external server)

  I feel ppl would like to include some sort of logging in capabilities
  on the router itself, which is more like nocat and less more my
  "solution" (unless "mpd" is installed on monowall)

  but tell, anyway. perhaps ppl can make suggestions/improve the idea,
  who knows?! :-)"


Josh