How to use the browserstack.source function in browserstack

notification.error({
            message: i18n.t('Error'),
            description: i18n.t('Perfecto SecurityToken is required'),
            duration: 4
          });
          return;
        }
        desiredCapabilities.securityToken = token;
        https = session.server.perfecto.ssl = false;
        break;
      case ServerTypes.browserstack:
        host = process.env.BROWSERSTACK_HOST || 'hub-cloud.browserstack.com';
        port = session.server.browserstack.port = 443;
        path = session.server.browserstack.path = '/wd/hub';
        username = session.server.browserstack.username || process.env.BROWSERSTACK_USERNAME;
        desiredCapabilities['browserstack.source'] = 'appiumdesktop';
        accessKey = session.server.browserstack.accessKey || process.env.BROWSERSTACK_ACCESS_KEY;
        if (!username || !accessKey) {
          notification.error({
            message: i18n.t('Error'),
            description: i18n.t('browserstackCredentialsRequired'),
            duration: 4
          });
          return;
        }
        https = session.server.browserstack.ssl = true;
        break;
      case ServerTypes.bitbar:
        host = process.env.BITBAR_HOST || 'appium.bitbar.com';
        port = session.server.bitbar.port = 443;
        path = session.server.bitbar.path = '/wd/hub';
        accessKey = session.server.bitbar.apiKey || process.env.BITBAR_API_KEY;