- By default, access is denied.
- Traffic destined for anywhere but to a select few services (i.e., TCP
  or UDP ports) is blocked by the local firewall.
  - NTP
  - IMAP(S)
  - POP(S)
  - OpenVPN
  - IPsec
- HTTP(S) traffic caught by firewall, redirected to the mesh node's
  client IP and port.
  - **iptables -t nat -A PREROUTING -i wlan0 -p tcp --dport 80 -j
    REDIRECT --to-port 31337**
  - **iptables -t nat -A PREROUTING -i wlan0 -p tcp --dport 443 -j
    REDIRECT --to-port 31338**
    - We'd have to add an extra bit in there **--destination 10.x.x.1**
- A web server listening on the redirect ports (31337/TCP and 31338/TCP)
  uses URI rewriting to point everything to a special URI:

` <VirtualHost *:31337>`
` RewriteEngine On`
` RewriteRule .* `[`https://byzantium.mesh/`](https://byzantium.mesh/)` [R,L]`
` `</VirtualHost>
` `
` <VirtualHost *:31338>`
` RewriteEngine On`
` RewriteRule .* `[`https://byzantium.mesh/`](https://byzantium.mesh/)` [R,L]`
` `</VirtualHost>

- The web server listening on ports 31337/TCP and 31338/TCP serves a
  page to the client. The client reads the text ("This is a wireless
  mesh, stuff about OPSEC, click here to pass through to the directory
  of services.") and clicks a button.
  - It'd be nice if the page also optionally displayed a message "There
    is a gateway to the public Net, so you can browse outside of this
    mesh." if a gateway route existed and had been propagated.
- When the button is clicked the firewall is updated to permit that MAC
  address to send traffic.
  - **[ipset](http://ipset.netfilter.org/) -A capo_sessions_ipset
    CLIENT_IP,CLIENT_MAC**
  - Yes, MAC spoofing to bypass this is trivial. This isn't to prevent
    people from getting online if they don't have a valid room number,
    it's to force them to see a message from the admin and then kick
    them over to a directory of services curated by the node's software.
- Set a timeout on the client IP? 10 minutes? 60 minutes? 5 minutes
  (same as DHCP lease time)?
  - **ipset -D capo_sessinos_ipset CLIENT_IP**
  - Captive::Portal includes a script (capo-ctl.pl) which already does
    this. In fact, you're supposed to run it from cron every ten minutes
    or so to clean out idle sessions.
- Captive::Portal requires iptables (have it), ipset (need to compile
  and install it), and a rule in */etc/sudoers* so it can run without
  privileges but still carry out privileged tasks.
- fping is used to test idle sessions (have it).
- A CGI script that implements a captive portal is included in
  Captive::Portal, it's called capo.cgi and runs under Apache.
- Basics of coding with this module:

` my $capo = Captive::Portal->new(cfg_file=>$cfg_file);`
` while (my $eq = CGI::Fast->new){`
`   $capo->run($q);`
` }`

- capo-ctl.pl is included with the module and manipulates the currently
  running IPtables rules (as well as backing store of Captive::Portal)
  with the ipset utility
- Everything Captive::Portal relies on the same configuration file (by
  default, config.pl).
- mock-server.pl is a script that pulls the HTML from a URI (say, a web
  server listening on wlan0) and spits it to stdout for testing.
- Used for testing your setup without needing a client.
- test-server.pl implements a very simple HTTP server so you can test
  your capi.cgi script without having to configure Apache.

<!-- -->

- We might have to modify capo.cgi to use the DBI Perl module to access
  the SQLite databases that hold the directories of services users can
  reach.
- We may have either modify or subclass the Captive::Portal class and
  add support for extracting and using the IP address of the client
  interface (wlan0:1) rather than just the physical interface (wlan0).
  It's been a long time since I've done OO under Perl but it's certainly
  possible.
- config.pl should be configured for no authentication (i.e., just a
  click-through).