tsa2Controller.php

<?php

namespace Drupal\tsa2\Controller;
use Drupal\Core\Url;
use Drupal\Component\Utility\Html;

use Drupal\Core\Controller\ControllerBase;

/**
 * Defines HelloController class.
 */
class tsa2Controller extends ControllerBase {

  /**
   * Display the markup.
   *
   * @return array
   *   Return markup array.
   */
  public function content() {
    // Default settings.
    $config = \Drupal::config('tsa2.settings');    
    $tsa2_api  = $config->get('tsa2_api');
    $element['#tsa2_api'] = Html::escape($tsa2_api);
    $element['#mainBody'] = $config->get('mainBody');
    $element['#theme'] = 'tsa2_theme';
    return $element;
  }

}