Wireguard configuration - PostUp and PostDown

[crodges]

Hello everyone,

I managed to configure wireguard on a vps running guix and created clients for 
my desktop and cellphone. What I want to do (and did already in a Debian vps) 
is to make wireguard's lan accessible to anyone connected and also browse the 
internet using this vpn.

As I remember, I need to allow ip forwarding using

sysctl net.ipv4.ip_forward=1

and I also need to put these rules into wireguard (the server) under 
[interface],

PostUp = iptables -A FORWARD -i wg0 -j ACCEPT; iptables -t nat -A POSTROUTING 
-o eth0 -j MASQUERADE; ip6tables -A FORWARD -i wg0 -j ACCEPT; ip6tables -t nat 
-A POSTROUTING -o eth0 -j MASQUERADE

PostDown = iptables -D FORWARD -i wg0 -j ACCEPT; iptables -t nat -D 
POSTROUTING -o eth0 -j MASQUERADE; ip6tables -D FORWARD -i wg0 -j ACCEPT; 
ip6tables -t nat -D POSTROUTING -o eth0 -j MASQUERADE

Problem is, looking at the latest guix manual, PostUp and PostDown doesn't 
seem to exist yet. Do they exist but are still undocumented?

If they don't exist, where should be a reasonable place to add this 
configurations? I'm trying to do everything the guix way, when I finish this 
machine configuration, I'd like it to be fully replicable.