I looked at your reference and the [Symfony documentation](http://symfony.com/doc/current/components/config/definition.html#normalization) and incorporated the following to Configuration.php:
1) Add the following line below line 103: ```->fixXmlConfig('header')```
2) Substitute my previous lines 118 to 122 for:
```php
->arrayNode('headers')
    ->useAttributeAsKey('name')
    ->prototype('scalar')->end()
->end()
```
I'm not entirely sure whether the line ```->useAttributeAsKey('name')``` is needed, but the code works with it or without it when testing it with the yml config indicated in the revised README (I'm able to connect to the authenticated client in both cases). Is that line needed? Is the rest of the code ok for you?