OH2: hue bridge: how to set the username?

When I define my hue bridge in a textual file like this:

Bridge hue:bridge:bridge1 [ ipAddress="" ] {
    LLC011 bulb1 [ lightId="1" ]
    LLC011 bulb2 [ lightId="2" ]

I don’t succeed to pair with my bridge. When I push the button, I have a log telling me to update manually the user name. So I try to update the configuration with Paper UI but it fails:

17:04:39.391 [INFO ] [ome.io.rest.core.thing.ThingResource] - Received HTTP PUT request for update configuration at 'things/hue:bridge:bridge1/config' for an unmanaged thing 'hue:bridge:bridge1'.
17:04:45.590 [WARN ] [binding.hue.handler.HueBridgeHandler] - User name for Hue bridge authentication not available in configuration. Setting ThingStatus to offline.

When I re-open the configuration in Paper UI, the user name is empty.
What’s wrong ?

If you define the brigde in the .things file, you cannot update it via PaperUI, as the .things file is read-only.
In this case, you have to add the username manually to the .things file like this:
Bridge hue:bridge:1 [ ipAddress="", userName="qwertzuiopasdfghjklyxcvbnm1234" ]

Check here for more information.