user_group.pp

define user_group (
  String $group,
  Enum['present', 'absent'] $ensure = 'present',
) {
  $changes = $ensure ? {
    'present' => "defnode ${group}/user[.='${name}'] '${name}'",
    'absent'  => "rm ${group}/user[.='${name}']",
  }

  augeas { "Manage ${title} in group ${group}":
    lens    => 'Group.lns',
    incl    => '/etc/group',
    changes => $changes,
  }
}