Permission to create new users but not to manage them

Question

I need to create a permission that allows any user to create other users without allowing them to manage all users (ie without granting them 'administer users' permission).

My approach was altering menu 'admin/people/create' but it - for unknown reason - doesn't work. Even though the permission for the menu is granted the menu item with link for is invisible and when I go to the specific url it - if I don't have 'administer users' permission - just redirects me to current user profile page.

    /**
 * Implements hook_menu_alter().
 */
function fm_users_more_menu_alter(&$items) {    
  $add_new_user = &$items['admin/people/create'];

  unset($add_new_user['access callback']);
  unset($add_new_user['access arguments']);

  $add_new_user['access callback'] = 'fmu_add_user_access_callback';
  $add_new_user['access arguments'] = array(1);
}

/**
 * Callback that manages access to create user page.
 */
function fmu_add_user_access_callback($arguement) {
  dsm('test23');
  return true;
}

It does the same - redirects you to current user profile page - with User register form.

  $register_new_user = &$items['user/register'];

  unset($register_new_user['access callback']);
  $register_new_user['access callback'] = 'fmu_register_user_access_callback';

/**
 * Callback that manages access to create user page.
 */
function fmu_register_user_access_callback() {
  dsm('test23');
  if (user_register_access() || user_access('create users under self')) {
    return true;
  }
  else {
    return false;
  }
}

Answer 1

Don't forget to also give those same users the permission to access administration pages -- otherwise they'll be denied anytime they try to access any URI beginning with admin.

Also, I don't think it's necessary (or even desirable) to unset the menu items like that... You should just be able to do this:

function fm_users_more_menu_alter(&$items) {    
  $items['admin/people/create']['access callback'] = 'fmu_add_user_access_callback';
  $items['admin/people/create']['access arguments'] = array(1);
}

Finally, remember to rebuild the menus after making such a change.

Answer 2

I've found out where the problem was, inside user register form there's this piece of code that - if a user is logged in but is not a administrator - redirects you to your profile page.

  // If we aren't admin but already logged on, go to the user page instead.
  if (!$admin && $user->uid) {
    drupal_goto('user/' . $user->uid);
  }

More information can be found here: https://api.drupal.org/api/drupal/modules!user!user.module/function/user_register_form/7