10_nm_dispatch_vpn_proxy

#!/bin/sh -e
# Script to set up the University of Hamburg web proxy when the Openconnect VPN connected
# credits to https://wiki.ubuntuusers.de/NetworkManager/Dispatcher/

VPN_CONNECTION_NAME="UniHH"
USER="UserNameHere"

# VPN connection started or stopped?
case "$2" in
    vpn-up)
	active_vpn=$(nmcli -t --fields NAME con show --active|grep "${VPN_CONNECTION_NAME}" -q)
	if $active_vpn; then
	    echo "UNI HH VPN started"
	    echo $(whoami)
	else
	    #Irrelevant VPN started, do nothing
	    exit 0
	fi
	# gsettings will fail if dbus is not launched with:
	# "dconf-WARNING **: failed to commit changes to dconf: Cannot autolaunch D-Bus without X11 $DISPLAY
	sudo -u "$USER" dbus-launch gsettings set org.gnome.system.proxy mode 'manual' 
	sudo -u "$USER" dbus-launch gsettings set org.gnome.system.proxy.http host 'proxy.uni-hamburg.de'
	sudo -u "$USER" dbus-launch gsettings set org.gnome.system.proxy.http port 3128
	##gsettings set org.gnome.system.proxy.ftp host 'proxy.localdomain.com'
	##gsettings set org.gnome.system.proxy.ftp port 3128
	sudo -u "$USER" dbus-launch gsettings set org.gnome.system.proxy.https host 'proxy.uni-hamburg.de'
	sudo -u "$USER" dbus-launch gsettings set org.gnome.system.proxy.https port 3128
	sudo -u "$USER" dbus-launch gsettings set org.gnome.system.proxy ignore-hosts "['localhost', '127.0.0.0/8', '10.0.0.0/8', '192.168.0.0/16', '172.16.0.0/12' , 'fc00::/8' , '*.fritz.box' ]"
        ;;
    vpn-down)
	# Disable all proxies on VPN shutdown, this might be to simple
	# for your case, it works for me.
	echo "VPN connection was stopped"
	sudo -u "$USER" dbus-launch gsettings set org.gnome.system.proxy mode 'none'
        ;;
esac

exit 0;

I am the first to admit that the multiple sudo dbus-launch constructs are ugly, but they were the first thing that actually worked. Improvements welcome :-)