additional customization of ApacheHttpClient e.g. for giving credentials

Currently it is not possible to customize HTTP client in a way which is not limited by DefaultApacheHttpClientConfig settings, so this additional configuration hook enables to e.g. set credentials to the HTTP client in following way:

override protected def doConfig(client: ApacheHttpClient) {
        client.addFilter(new HTTPBasicAuthFilter(auth.user, auth.password))
}