private function addClientSection(ArrayNodeDefinition $node)
    {
        $node
            ->children()
                ->arrayNode('client')
                    ->children()
                        ->scalarNode('application_name')->isRequired()->cannotBeEmpty()->end()
                        ->scalarNode('client_id')->end()
                        ->scalarNode('client_secret')->end()
                        ->scalarNode('redirect_uri')->end()
                        ->scalarNode('developer_key')->end()
                    ->end()
                ->end()
            ->end()
        ;
    }