Default grou membership for new users

[Christoph Wickert]

Hi there,

I am looking for a way how to add new users to a certain group upon
creation. Do we have such a mechanism?

/etc/default/useradd only is for useradd and can set a default group,
but no additional default groups.

Background: The 'Fedora Jam' spin [1] requires users to be in the groups
'audio' and 'jackuser'. This can be hacked for the liveuser in the
livesys initscript, but what about other users, e.g. the one that gets
created with firstboot.

The spin owner had a dirty hack that modified 
/usr/share/firstboot/modules/create_user.py, but as the spins wrangler I
told him  this is a no-go.

Kind regards,
Christoph

[1] https://fedoraproject.org/wiki/Fedora_jam