Setting Roles
Setting roles on a group is simple. All you need to do is set the roles attribute when adding or updating a group:
When Adding a Group
$group = array(
'name' => 'Test Group',
'description' => 'This is a test group.',
'roles' => array('new_role_1', 'new_role_2')
);
$this->bitauth->add_group($group);
The example included in the BitAuth download gives an example of how to do this easily with an HTML form.
When Updating a Group
$group = $this->bitauth->get_group_by_name('Test Group');
$group->roles = array('new_role_1', 'new_role_2');
$this->bitauth->update_group($group->group_id, $group);
Any changes you make to group roles are reflected in all members of that group the next time they log in.