LdapUserBackend: Provide filter column `user'

refs #8826

library/Icinga/Authentication/User/LdapUserBackend.php

@@ -42,6 +42,13 @@ class LdapUserBackend extends Repository implements UserBackendInterface
      */
     protected $filter;
 
+    /**
+     * The columns which are not permitted to be queried
+     *
+     * @var array
+     */
+    protected $filterColumns = array('user');
+
     /**
      * The default sort rules to be applied on a query
      *
@@ -250,6 +257,7 @@ class LdapUserBackend extends Repository implements UserBackendInterface
             }
 
             $this->queryColumns[$this->userClass] = array(
+                'user'          => $this->userNameAttribute,
                 'user_name'     => $this->userNameAttribute,
                 'is_active'     => 'unknown', // msExchUserAccountControl == 2/512/514? <- AD LDAP
                 'created_at'    => 'whenCreated', // That's AD LDAP,