code: public function addConfiguration(NodeDefinition $node)
      {
          $node
              ->children()
                  ->scalarNode('curve')
                      ->validate()
                          ->ifTrue(self::checkCurve())
                          ->thenInvalid('Unsupported curve. Please use "P-256", "P-384" or "P-521".')
                      ->end()
                      ->isRequired()
                  ->end()
              ->end();
          parent::addConfiguration($node);
      }
docs: {@inheritdoc}