code: private function addHostToContext(RequestContext $context, array $parameters, int &$referenceType): void
      {
          [$host, $port] = $this->getHostAndPort($parameters['_domain']);
  
          if ($context->getHost() === $host) {
              return;
          }
  
          $context->setHost($host);
          $referenceType = UrlGeneratorInterface::ABSOLUTE_URL;
  
          if (!$port) {
              return;
          }
  
          if (isset($parameters['_ssl']) && true === $parameters['_ssl']) {
              $context->setHttpsPort($port);
          } else {
              $context->setHttpPort($port);
          }
      }
docs: Sets the context from the domain.