Make user selection configurable (displayed field) + ajaxify it

[tlartaud]

See https://wp-customerarea.com/support/topic/problem-adding-users-to-a-group/

[vpratfr]

User selection needs some work all over the plugin.

In this case, we are missing a filter to allow customizing the user list (that would allow to show something else than the display name)

customer-area-extended-permissions\src\php\user-group\user-group-admin-interface.class.php line 199

BUT

We also need to allow picking a user using an Ajax search: our current approach starts causing problems when there are a few hundreds of users (page time is too long).

So we need to think about this issue in the next release. Ideally, user selection will be made standard (one single access point for the whole plugin): use ajax whenever there is a select2 for user (owners, admin filter, switch users, groups, projects, etc.)

[vpratfr]

@tlartaud

Would be nice to add a post snippet to show how to customize the way owners are displayed. For example, show email instead of display_name for users.

###How to do that?

use the filter: cuar/core/ownership/owner-display-name?owner-type={{owner_type}} where {{owner_type}} is one of usr, grp, mgrp, prj, rol, sgrp, glo

The function used by the filter receives the default value and the owner id as parameters.

For instance (not tested):

function cuar_change_user_display_info($default, $id) {
    $user = new WP_User($id);
    return $user->email;
}
add_filter('cuar/core/ownership/owner-display-name?owner-type=usr', 'cuar_change_user_display_info', 10, 2)

[vpratfr]

Fixed

[vpratfr]

Reopened until @tlartaud creates the code snippet