How to mark packets on one server in order to filter them on another?

Question

Mikrotik

Good day!
There is a Privoxy proxy server open to all winds, to which http requests are pouring from Mikrotik routers. It is required to somehow mark packets on the router so that only they are accepted on the proxy server, and all others are blocked.
There are many routers and ip-addresses can be dynamic and difficult to track (that is, a filtering method by addresses is undesirable).

Answer 1

packet marking does not go beyond the router, look for another option.
I would suggest raising the tunnel and only accept requests coming through the tunnel. Well, send the necessary requests to the tunnel - this can already be done on Mikrotik

Answer 2

you can try to set and catch QoS
marker example