Cannot enable MQTT authenticated mode for multiple users

Alarm system

EVO192 v.7.70.1

Environment

Rpi/docker

Git branch

master

Question

I'm trying to enable MQTT authenticated mode for multiple users, but the docker container fails at startup.

MQTT_CHALLENGE_SECRET = {'foo': 'bar'}
MQTT_CHALLENGE_ROUNDS = 10000

However, it starts regularly when using a single secret.

MQTT_CHALLENGE_SECRET = 'foo'
MQTT_CHALLENGE_ROUNDS = 10000

What's wrong with the first one?

Logs (if required)

Attempting to load configuration from /etc/pai/pai.conf
Error parsing configuration: Invalid value type <class 'dict'> for config argument MQTT_CHALLENGE_SECRET. Allowed are: [<class 'str'>, <class 'NoneType'>]