code: public function getNodeDefinition(ArrayNodeDefinition $node)
      {
          $sourceNodeBuilder = $node
              ->children()
                  ->arrayNode('keys')
                      ->useAttributeAsKey('name')
                      ->prototype('array')
                          ->performNoDeepMerging()
                          ->children();
          foreach ($this->getJWKSources() as $name => $source) {
              $sourceNode = $sourceNodeBuilder->arrayNode($name)->canBeUnset();
              $source->addConfiguration($sourceNode);
          }
      }
docs: {@inheritdoc}