maybe we should move the definition of which class to use to the plugin?

```php
function restful_plugin_process(&$plugin, $info) {
    if ($info['type'] == 'restful') {
      $plugin += array(
        'description' => '',
        'options' => array(),
        'auth_manager' => '\RestfulAuthenticationManager',
        'cache_controller' => NULL
```

Anyway, it can be in a follow up PR