How to set an external proxy server on OpenWRT?

Question

linux

I have several routers with OpenWRT firmware. I want all their external network traffic to pass through my server, so that I can control and log it.
Example: a person connects to a network, and the first time he accesses the Internet through this network, he will see my page on which he must enter a password for further access. How to configure all this on the server side is not important now.
How to redirect all external traffic to a specific ip? I do not see a way, except through the DNS server.

Answer 1

Well, in my opinion, it is logical to organize this with vpn tunnels.
Each router clings to your server via vpn and all traffic accordingly goes through it (keep in mind that the channel in this case must be wide).
Regarding the first connection and advertising page, google in the direction of "Captiv portal".

Answer 2

it is possible to forward certain ports to a "transparent proxy"
But, if memory serves me right, squid in transparent proxy mode does not work with authorizations.
Although it may have already been done.
squid transparent authorization