Guzzle Oauth current state

Controller.php

<?php

/**
 * @file
 * Contains \Drupal\sf_test\Controller\DefaultController.
 */

namespace Drupal\sf_test\Controller;

use Drupal\Core\Controller\ControllerBase;
use GuzzleHttp\Exception\ClientException;

/**
 * Class DefaultController.
 *
 * @package Drupal\sf_test\Controller
 */
class DefaultController extends ControllerBase {
  /**
   * Hello.
   *
   * @return string
   *   Return Hello string.
   */
  public function hello() {
    // Get the HTTP Client Factory so that custom options can be added.
    $factory = \Drupal::service('http_client_factory');
    $client = $factory->fromOptions([
      'base_uri' => 'https://api.twitter.com',
      'auth' => 'oauth', // <--- magic !!
    ]);
    try {
      $response = $client->get('1.1/statuses/user_timeline.json');
      $tweets = var_export(json_decode($response->getBody()), TRUE);
    }
    catch (ClientException $e) {
      $tweets = $e->getMessage();
    }

    return [
      '#type' => 'markup',
      '#prefix' => '<pre>',
      '#markup' => $tweets,
      '#suffix' => '</pre>',
    ];
  }

}

guzzle_oauth.services.yml

services:
  guzzle_oauth.factory:
    class: Drupal\guzzle_oauth\OauthFactory
    arguments: ['@config.factory']
  guzzle_oauth.middleware:
    class: GuzzleHttp\Subscriber\Oauth\Oauth1
    factory: guzzle_oauth.factory:getService
    tags:
      - { name: http_client_middleware } # <-- magic

guzzle_oauth.settings.yml

consumer_key: "consumer_key"
consumer_secret: "consumer_secret"
token: "token"
token_secret: "token_secret"

OauthFactory.php

<?php

/**
 * @file
 * Contains \Drupal\guzzle_oauth\OauthFactory.
 */

namespace Drupal\guzzle_oauth;

use Drupal\Core\Config\ConfigFactory;
use GuzzleHttp\Subscriber\Oauth\Oauth1;

/**
 * Class OauthFactory
 */
class OauthFactory {

  /**
   * @var \Drupal\Core\Config\Config|\Drupal\Core\Config\ImmutableConfig
   */
  protected $config;

  /**
   * OauthFactory constructor.
   *
   * @param \Drupal\Core\Config\ConfigFactory $configFactory
   */
  function __construct(ConfigFactory $configFactory) {
    $this->config = $configFactory->get('guzzle_oauth.settings');
  }

  /**
   * @return Oauth1
   */
  public function getService() {
    return new Oauth1((array) $this->config->get());
  }

}