added config settings in service factory class for getting comScore credentials.

  public static function createInstance() {

    static $instance = null;

    if($instance === null) {

      $soap_client = $client = new SoapClient('https://api.comscore.com/ReachFrequency/CampaignRf.asmx?WSDL', array(

        'login' => '',

        'password' => '',

      //for getting comScore credentials.

      $config = \Drupal::config('comscore_analytics.settings');

      $login = $config->get('comscore_analytics_account');

      $password = $config->get('comscore_analytics_password');

      $reach_frequency_endpoint = \Drupal::config('comscore_analytics.settings')->get('comscore_endpoint_reach_frequency');

      $soap_client = $client = new SoapClient($reach_frequency_endpoint, array(

        'login' => $login,

        'password' => $password,

      ));

      $instance = new ComscoreService($soap_client);

    }