Using the Alfen servicetool I managed to sniff the port 80 traffic to the charger.
Example:
~/Projects/AlfenLaadpaal$ python3 -i alfencharger.py
>>> lp = AlfenCharger('10.4.101.119', 'admin', 'see-capture-wireshark')
>>> lp.get_charge_status()
{'max_current': 23.0, 'socket_state': 'idle'}
>>> lp.set_charge_current(24)
True
>>> lp.get_charge_status()
{'max_current': 24.0, 'socket_state': 'idle'}