Autor darf nur bestimmte Benutzergruppen hinzufügen

<?php
/*
    Plugin Name: Role Manager Security Patch
    Plugin URI: http://www.im-web-gefunden.de/wordpress-plugins/role-manager/
    Description: Add-On to Role Manager plugin to use WP API to better control the editing of users by other users.
    Specifically to avoid users having the ability to change their role to administrator when they are give the edit_users privilege.
    Version: 2.2.1
    Author: Jeremy Clarke
    Author URI: http://www.im-web-gefunden.de/
    Update Server:  http://www.im-web-gefunden.de/
    Min WP Version: 2.0
    Max WP Version: 2.3
    License: MIT License - http://www.opensource.org/licenses/mit-license.php
*/


// ***************************************************************
// Remove any role that has a capability that the current user doesn't have.
// 
// uses the 'editable_roles' filter which might not exist yet. Probably
// won't be around until 2.6 is released, maybe 2.5.1...
//


function filter_editable_roles($roles) {
    foreach ($roles as $role => $details) :
        foreach ($details['capabilities'] as $capability => $value) :
            if (!current_user_can($capability)) :
                unset ($roles[$role]);
                break;
            endif; 
        endforeach; //capabilities
    endforeach; //foreach $wp_roles;
    return $roles;
}
add_filter('editable_roles', 'filter_editable_roles');






// ***************************************************************
// Check if the logged in user should be allowed to edit another
// user. 
//
// For hooking into 'user_has_cap' filter. Use when doing a 
// check for current_user_can('edit_user', $user_id);
// Works by comparing the logged-in user to the $user_object,
// if $user_object has any capability that the logged-in user DOESN'T
// then the edit is denied. 
//
// NOTE: this won't help stopping users from being PROMOTED to an 
// innapropriate role. For that the promotion logic needs to get
// the filtered roles with get_editable_roles
//
// $allcaps - a copy of $wp_roles->role_names , it should return with
//          innapropriate roles removed.
            
function check_user_editable($allcaps, $caps, $args) {
    // only run if we're checking the 'edit_users' cap
    // also, only if there is a second argument in $args (the second, edited, user)
    if ($caps[0] == 'edit_users' && $args[2]) :
        
        // Get full information about the user that they want to edit.
        global $user_object, $wp_roles;
        
        // The $user_object variable is often not available when checks like this are made. 
    
        // line 109 of /wp-admin/user-edit.php 
        
    
        // Not doing that yet though, for now we'll just
        // return the list as before if the $user_object doesn't have the 
        // same ID as the argument that was passed into the filter
        
        if (!$user_object) $user_object = new wp_user($args[2]);




        if ($user_object->ID != $args[2]) return $allcaps;
        
        $edited_user_caps = $user_object->allcaps;
        $edited_user_roles = $user_object->roles;
        $checked_roles = array();


        // go through edited user's roles, and check for missing caps. 
        foreach ($edited_user_roles as $role => $name) :
            $rolecaps = $wp_roles->roles[$name]['capabilities'];
            foreach($rolecaps as $capability => $value) :
                if (!current_user_can($capability)) :
                    unset ($allcaps['edit_users']);
                    return $allcaps;
                endif; 
            endforeach; // rolecaps
            // add the role to a list of checked roles if there are no problems
            $checked_roles[] = $name;
        endforeach; // foreach edited_user_roles
        
        // This only runs if there were no conflicts while checking roles
        // go through the edited users caps and check if current user has them all
        foreach ($edited_user_caps as $capability => $value) :
            if (in_array($capability, $checked_roles)) :
                continue;
            elseif (!current_user_can($capability)) :
                unset ($allcaps['edit_users']);
                return $allcaps;
            endif; 
        endforeach; //capabilities    
    endif;// if edit_users
     
    return $allcaps;
}


add_filter('user_has_cap', 'check_user_editable', 10, 3)
?>