implementing port forward restrictions

[michael salmon]

hi folks,
right now im implementing a quick hack to restrict ports the server will 
allow to be forwarded. This is to heighten security from clients accessing a 
server behind a firewall and as far as I could tell this is not possible with 
ssh so far. 
I think this is a reasonable feature for a release and shouldnt be too hard 
to implement in a way that follows the setup already used in the config and 
sshd handling of connections. I searched the mailing-list archives and found 
a few small references to it but none implied it was being worked on.
When I finish this if the list wants the diffs I'd be happy to supply them. 
I'd like the opinion of the other developers as to a key in the sshd_config 
that would be obvious yet not too long to define the ports, and the layout.
I was thinking 
HostAllowsPortsForwarded 143 2401 etc... space delimited numbers.

cheers,
michael salmon