Created rest endpoint to list existing domains

module/Rest/src/Action/Domain/ListDomainsAction.php

@@ -0,0 +1,52 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\Rest\Action\Domain;
+
+use Laminas\Diactoros\Response\JsonResponse;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Shlinkio\Shlink\Core\Domain\DomainServiceInterface;
+use Shlinkio\Shlink\Core\Entity\Domain;
+use Shlinkio\Shlink\Rest\Action\AbstractRestAction;
+
+use function Functional\compose;
+use function Functional\map;
+
+class ListDomainsAction extends AbstractRestAction
+{
+    protected const ROUTE_PATH = '/domains';
+    protected const ROUTE_ALLOWED_METHODS = [self::METHOD_GET];
+
+    private DomainServiceInterface $domainService;
+    private string $defaultDomain;
+
+    public function __construct(DomainServiceInterface $domainService, string $defaultDomain)
+    {
+        $this->domainService = $domainService;
+        $this->defaultDomain = $defaultDomain;
+    }
+
+    public function handle(ServerRequestInterface $request): ResponseInterface
+    {
+        $regularDomains = $this->domainService->listDomainsWithout($this->defaultDomain);
+
+        return new JsonResponse([
+            'domains' => [
+                'data' => [
+                    $this->mapDomain($this->defaultDomain, true),
+                    ...map($regularDomains, fn (Domain $domain) => $this->mapDomain($domain->getAuthority())),
+                ],
+            ],
+        ]);
+    }
+
+    private function mapDomain(string $domain, bool $isDefault = false): array
+    {
+        return [
+            'domain' => $domain,
+            'isDefault' => $isDefault,
+        ];
+    }
+}