I don't really see a way to do that in a clean way yet.

```php
$idpEntityId = $this->handleArguments(func_get_args(), array('vo', 'key'), $proxyServer, true);
```

or

```php
$handler = new ArgumentHandler($proxyServer);
$handler->useVo();
$handler->useKey()
$idpEntityId = $handler->process(func_get_args());
```

I don't see enough commonality yet.