MQTT authentication problem

I have installed Chirpstack 4.17.0 on Ubuntu 24.xx.
It worked fine, but now I am trying to button down security just a little, and have the following problem : when I enable mosquitto security (disallowing anonymous access and setting a password file), nothing works and the mosquitto-log fills up with : 
1783586509: Client d21f3609142423dd disconnected, not authorised.
1783586509: New connection from 127.0.0.1:40228 on port 1883.
1783586509: Client eb7b8e42b842898b disconnected, not authorised.
1783586509: New connection from 127.0.0.1:40234 on port 1883.
1783586509: New connection from 127.0.0.1:40238 on port 1883.
1783586509: Client 4ae9385d7b577d46 disconnected, not authorised.
...

I HAVE tested the username and password with mosquitto_sub and it works.


/etc/chirpstack-gateway-bridge/chirpstack-gateway-bridge.toml :

  # MQTT authentication.
  [integration.mqtt.auth]
  # Type defines the MQTT authentication type to use.
  #
  # Set this to the name of one of the sections below.
  type="generic"

    # Generic MQTT authentication.
    [integration.mqtt.auth.generic]
    # MQTT server (e.g. scheme://host:port where scheme is tcp, ssl or ws)
    server="tcp://127.0.0.1:1883"

    # Connect with the given username (optional)
    username="alftest"

    # Connect with the given password (optional)
    password="12345"



    /etc/chirpstack/chirpstack.toml:

[integration]
  enabled = ["mqtt"]

  [integration.mqtt]
    server = "tcp://127.0.0.1:1883/"
    json = true
    username = "alftest"
    password = "12345"