What is the modern way to do port-forwarding on El Capitan? (forward port 80 to 8080)
To forward all port 80 traffic to port 8080, you can enter the following from the Terminal command line.

echo "
rdr pass inet proto tcp from any to any port 80 -&gt; 127.0.0.1 port 8080
" | sudo pfctl -ef -


Taken from https://salferrarello.com/mac-pfctl-port-forwarding/