Максим Мельник

Переменная
$_SERVER['HTTP_HOST']
вполне успешно решает эту задачу.

Вот пример моего решения, которое работает без нареканий:

TargetUrlParser.php

namespace App\Url;


class TargetUrlParser
{
  /**
   * Get target url
   *
   * @return string
   */
  public static function getUrl()
  {
    return (string) $_SERVER['HTTP_HOST'];
  }
}

HomePageController.php

class HomePageController extends Controller
{
  /**
   * @var Site
   */
  private $site = null;

  /**
   * @var SiteSettings
   */
  private $siteSettings = null;

  /**
   * HomePageController constructor.
   */
  public function __construct()
  {
    $this->site = Site::where('http_host', '=', TargetUrlParser::getUrl())->firstOrFail();
    $this->siteSettings = (new SiteSettingsFactory($this->site))->createSiteSettings();
  }

  public function index()
  {
    return view('pages.index')->with(['settings' => $this->siteSettings, 'site' => $this->site]);
  }
}

Миграция для модели Site.php

class CreateSitesTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('sites', function (Blueprint $table) {
            $table->increments('id');
            $table->string('http_host');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('sites');
    }
}