Document guest tokens

Closes #439

Author: BurntimeX

docs/javascript/components_guest_token.md

@@ -0,0 +1,63 @@
+# Guest Token
+
+Guest token is a generic implementation to handle the authorization of a guest (entering a user name and filling out a captcha) that can be used in various places.
+
+The token must be transmitted to the backend and validated there. A corresponding API is available on the PHP backend.
+
+## Client-side Example
+
+```ts
+import { prepareRequest } from "WoltLabSuite/Core/Ajax/Backend";
+import User from "WoltLabSuite/Core/User";
+import { getGuestToken } from "WoltLabSuite/Core/Component/GuestTokenDialog";
+
+let token: string | undefined = "";
+if (!User.userId) {
+  token = await getGuestToken();
+}
+
+await prepareRequest("your_backend_url").post({
+  token,
+}).fetchAsJson();
+```
+
+## Backend Example
+
+```php
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use wcf\http\Helper;
+use wcf\system\endpoint\IController;
+use wcf\system\endpoint\PostRequest;
+use wcf\system\exception\UserInputException;
+use wcf\system\WCF;
+use wcf\util\UserUtil;
+
+#[PostRequest('/core/foo')]
+final class CreateFoo implements IController
+{
+    public function __invoke(ServerRequestInterface $request, array $variables): ResponseInterface
+    {
+        $parameters = Helper::mapApiParameters($request, CreateFooParameters::class);
+        
+        $username = '';
+        if (!WCF::getUser()->userID) {
+            $username = UserUtil::verifyGuestToken($parameters->guestToken);
+            if ($username === null) {
+                throw new UserInputException('guestToken');
+            }
+        }
+
+        // ...
+    }
+}
+
+/** @internal */
+final class CreateFooParameters
+{
+    public function __construct(
+        public readonly string $guestToken,
+    ) {
+    }
+}
+```

mkdocs.yml

@@ -64,6 +64,7 @@ nav:
           - 'Confirmation': 'javascript/components_confirmation.md'
           - 'Dialog': 'javascript/components_dialog.md'
           - 'Google Maps': 'javascript/components_google_maps.md'
+          - 'Guest Token': 'javascript/components_guest_token.md'
           - 'Notices': 'javascript/components_notice.md'
           - 'Pagination': 'javascript/components_pagination.md'
           - 'RPC API': 'javascript/components_rpc_api.md'