code: public static function getAccessToken()
      {
          $oauthClientParams = ArrayHelper::getValue(\Yii::$app->params, 'oauth');
          $oauthClient = new Oauth2Client($oauthClientParams);
          $code = $oauthClient->authorize();
          $token = $oauthClient->fetchAccessToken($code);
          $accessToken = ArrayHelper::getValue($token, 'access_token');
          return $accessToken;
      }
docs: Returns the access token
  @author Adegoke Obasa <goke@cottacush.com>
  @return mixed