That is correct. There is a trick where you can set the source ip to the ipv6 mapped ipv4 ip it originally came from. I have implemented that in a transparent tcp proxy I worked on some years ago, but I am not sure if nginx supports that.

I should look into that actually. It would be useful to me as well.

Edit: actually that only works if you are in the routing path. However a nat64 solution would work as well, where you map a /64 back to the proxy.

It’s merely a tcp proxy. It doesn’t even have to be http since it has no idea. The trick with tls is that it can extract the requested host name via SNI.

Or just use Nginx stream proxy, and all the encryption happens on the endpoints. No need for certs on the proxy at all.

This is how I make https and mqtts available on ipv4.