Is it possible and how to configure a proxy that works for a specific ubuntu network device?

Question

Computer networks

How can I set up a proxy on ubuntu that will only work for a specific network device?
The essence of the problem. There are 2 data channels. One is secure, which requires a SOCKS5 proxy to work, the second is open and without protection. It is necessary to drive traffic from these two interfaces to the other two, from the unsecured one (which preliminarily raises pppoe) to the unsecure one, from the protected one with a proxy, already drive traffic after the proxy.

Answer 1

iptables -j MARK + iproute2

Answer 2

3proxy can do it out of the box