Catch and forward traffic destined for specific host

Install socat

apt install socat

Create IPtables NAT rules

iptables -t nat -N REDCAP_SOCAT
iptables -t nat -A REDCAP_SOCAT -p tcp -d 160.129.8.154 --dport 443 -j REDIRECT --to-ports 12345
iptables -t nat -A OUTPUT -p tcp -d 160.129.8.154 --dport 443 -j REDCAP_SOCAT

Test socat in foregroud (160.129.8.154 – is IP of redcap.vumc.org)

socat TCP4-LISTEN:12345,fork,reuseaddr PROXY:your_proxy.ca:redcap.vumc.org:443,proxyport=3128

make it permanent/create service

touch /etc/systemd/system/socat-redcap-proxy.service

content of socat-redcap-proxy.service

[Unit]
Description=Socat proxy tunnel for redcap.vumc.org via your_proxy.ca:3128
After=network.target

[Service]
ExecStart=/usr/bin/socat TCP4-LISTEN:12345,fork,reuseaddr PROXY:your_proxy.ca:redcap.vumc.org:443,proxyport=3128
Restart=always
RestartSec=5
StandardOutput=journal
StandardError=journal

[Install]
WantedBy=multi-user.target

Enable it

systemctl daemon-reexec
systemctl daemon-reload
systemctl enable --now socat-redcap-proxy

enjoy