Automatically configure APT to use proxies based on the currently used network. Script can be run for example by the NetworkManger dispatch mechanism.
Copy or symlink the file to /etc/NetworkManager/dispatch.d/99SetAptProxy and make sure it is executable there.
The configuration file /etc/apt-proxies consists of one line per network in the format <search domain> <host> <port>. The network is specified by its search domain found in /etc/resolv.conf. The APT cache service is located by the given hostname and port.
Finding the current network via the search domain from /etc/resolv.conf can be problematic, when NetworkManager uses its own builtin dnsmasq caching name server.