diff --git a/README.md b/README.md
index 84c721f..f1487bf 100644
--- a/README.md
+++ b/README.md
@@ -33,12 +33,12 @@ to deliver files and generate cached thumbnails.
 
 ## Important security note
 
-The file-serving endpoint is designed for convenience and caching and does NOT
-apply DokuWiki ACLs. Anything reachable through a configured root may be
-accessible to anyone who can access your wiki and guess/copy the generated URLs.
+The file-serving endpoint (`lib/plugins/luxtools/file.php`) runs inside DokuWiki
+and can enforce a simple access restriction based on the currently logged-in
+user.
 
-Only configure roots that contain non-sensitive data, or protect access on the
-webserver/network level.
+This is intentionally *not* full per-page ACL integration; it is a pragmatic
+allowlist to avoid “anyone with a guessed URL can fetch the file”.
 
 
 ## Installation
@@ -60,6 +60,13 @@ luxtools is configured via its dedicated admin page:
 
 Key settings:
 
+- **access_allow**
+  Allowed users/groups for the file-serving endpoint.
+  - Entries can be separated by newlines, commas, or whitespace.
+  - Use `@group` to allow a whole group.
+  - Leave empty to allow any authenticated (logged-in) user.
+  - Anonymous users are always denied.
+
 - **paths**
   Allowed base filesystem roots (one per line). Each root can be followed by:
   - `A> /Alias/` (optional) alias used in wiki syntax and open links
@@ -77,6 +84,10 @@ Key settings:
 
   `lib/plugins/luxtools/file.php?root=...&file=...`
 
+  Note: if you configure a `W>` web URL to an external file server, that server
+  must enforce access itself; DokuWiki ACLs and `access_allow` only apply to
+  `file.php`.
+
 - **scratchpad_paths**
   Scratchpad file map (one file path per line, followed by an `A>` alias line).
 
diff --git a/admin/main.php b/admin/main.php
index 447f7d7..ccae556 100644
--- a/admin/main.php
+++ b/admin/main.php
@@ -10,6 +10,7 @@ class admin_plugin_luxtools_main extends DokuWiki_Admin_Plugin
 {
     /** @var string[] */
     protected $configKeys = [
+        'access_allow',
         'paths',
         'scratchpad_paths',
         'allow_in_comments',
@@ -48,6 +49,10 @@ class admin_plugin_luxtools_main extends DokuWiki_Admin_Plugin
         }
 
         $newConf = [];
+        $accessAllow = $INPUT->str('access_allow');
+        $accessAllow = str_replace(["\r\n", "\r"], "\n", $accessAllow);
+        $newConf['access_allow'] = $accessAllow;
+
         // Normalize newlines to "\n" for consistent parsing
         $paths = $INPUT->str('paths');
         $paths = str_replace(["\r\n", "\r"], "\n", $paths);
@@ -88,6 +93,12 @@ class admin_plugin_luxtools_main extends DokuWiki_Admin_Plugin
         echo '<fieldset>';
         echo '<legend>' . hsc($this->getLang('legend')) . '</legend>';
 
+        // access_allow: multiline (users/groups)
+        $accessAllow = (string)$this->getConf('access_allow');
+        echo '<label class="block"><span>' . hsc($this->getLang('access_allow')) . '</span><br />';
+        echo '<textarea name="access_allow" rows="3" cols="80" class="edit">' . hsc($accessAllow) . '</textarea>';
+        echo '</label><br />';
+
         // paths: multiline textarea
         $paths = (string)$this->getConf('paths');
         echo '<label class="block"><span>' . hsc($this->getLang('paths')) . '</span><br />';
diff --git a/conf/default.php b/conf/default.php
index db9d9a9..f857255 100644
--- a/conf/default.php
+++ b/conf/default.php
@@ -19,3 +19,8 @@ $conf['gallery_thumb_scale'] = 1;
 
 // Local client service used by {{open>...}}.
 $conf['open_service_url'] = 'http://127.0.0.1:8765';
+
+// Access allowlist for the file-serving endpoint (file.php).
+// Empty means: any authenticated user may access. Anonymous users are denied.
+// Use '@group' to allow a whole group.
+$conf['access_allow'] = '';
diff --git a/file.php b/file.php
index f680c67..bbed9bf 100644
--- a/file.php
+++ b/file.php
@@ -5,7 +5,6 @@
 use dokuwiki\plugin\luxtools\Path;
 
 if (!defined('DOKU_INC')) define('DOKU_INC', __DIR__ . '/../../../');
-if (!defined('NOSESSION')) define('NOSESSION', true); // we do not use a session or authentication here (better caching)
 if (!defined('DOKU_DISABLE_GZIP_OUTPUT')) define('DOKU_DISABLE_GZIP_OUTPUT', 1); // we gzip ourself here
 require_once(DOKU_INC . 'inc/init.php');
 
@@ -14,9 +13,91 @@ global $INPUT;
 $syntax = plugin_load('syntax', 'luxtools');
 if (!$syntax) die('plugin disabled?');
 
+/**
+ * Enforce a simple allowlist based access check.
+ *
+ * The allowlist supports entries separated by commas, whitespace or newlines.
+ * - "alice" allows a specific user
+ * - "@admins" allows a DokuWiki group
+ *
+ * If the allowlist is empty, any authenticated user is allowed.
+ * Anonymous access is always denied.
+ *
+ * @param string $allowListRaw
+ * @return void
+ */
+function luxtools_require_access(string $allowListRaw): void
+{
+    global $INPUT, $USERINFO;
+
+    // We need a logged-in user for any access.
+    $user = '';
+    try {
+        $user = (string)$INPUT->server->str('REMOTE_USER');
+    } catch (Throwable $e) {
+        $user = (string)($_SERVER['REMOTE_USER'] ?? '');
+    }
+    $user = trim($user);
+
+    if ($user === '') {
+        header('Content-Type: text/plain; charset=utf-8');
+        http_status(403);
+        echo 'forbidden';
+        exit;
+    }
+
+    $allowListRaw = trim($allowListRaw);
+    if ($allowListRaw === '') {
+        return; // any authenticated user
+    }
+
+    $tokens = preg_split('/[\s,;]+/', $allowListRaw, -1, PREG_SPLIT_NO_EMPTY);
+    if (!is_array($tokens) || $tokens === []) {
+        // If configured but empty after parsing, be conservative.
+        header('Content-Type: text/plain; charset=utf-8');
+        http_status(403);
+        echo 'forbidden';
+        exit;
+    }
+
+    $groups = [];
+    if (is_array($USERINFO) && isset($USERINFO['grps']) && is_array($USERINFO['grps'])) {
+        $groups = $USERINFO['grps'];
+    }
+
+    $allowed = false;
+    foreach ($tokens as $t) {
+        $t = trim((string)$t);
+        if ($t === '') continue;
+
+        if ($t[0] === '@') {
+            $g = trim(substr($t, 1));
+            if ($g !== '' && in_array($g, $groups, true)) {
+                $allowed = true;
+                break;
+            }
+        } else {
+            if ($t === $user) {
+                $allowed = true;
+                break;
+            }
+        }
+    }
+
+    if (!$allowed) {
+        header('Content-Type: text/plain; charset=utf-8');
+        http_status(403);
+        echo 'forbidden';
+        exit;
+    }
+}
+
 $pathUtil = new Path($syntax->getConf('paths'));
 $path = $INPUT->str('root') . $INPUT->str('file');
 
+// Enforce access before doing any filesystem work.
+luxtools_require_access((string)$syntax->getConf('access_allow'));
+
 /**
  * Send a file to the client with basic caching headers.
  *
@@ -47,7 +128,8 @@ function luxtools_sendfile($path, $mime, $download = false, $downloadName = null
     }
 
     if ($maxAge !== null) {
-        header('Cache-Control: public, max-age=' . (int)$maxAge . ', immutable');
+        // Authentication may apply; keep caching private.
+        header('Cache-Control: private, max-age=' . (int)$maxAge . ', immutable');
     }
 
     // Conditional request handling
diff --git a/lang/de/lang.php b/lang/de/lang.php
index 9bf34d0..3f0896a 100644
Binary files a/lang/de/lang.php and b/lang/de/lang.php differ
diff --git a/lang/en/lang.php b/lang/en/lang.php
index 02f606b..7d85da7 100644
--- a/lang/en/lang.php
+++ b/lang/en/lang.php
@@ -25,6 +25,8 @@ $lang['saved'] = 'Settings saved.';
 $lang['err_save'] = 'Could not save settings. Please check write permissions for conf/local.php.';
 $lang['err_security'] = 'Security token mismatch. Please retry.';
 
+$lang['access_allow'] = 'Allowed users/groups for file access (one per line or comma-separated). Use @group for groups. Leave empty to allow any logged-in user.';
+
 $lang['paths'] = 'Allowed base paths (one per line). Optional: follow a path with A> alias and W> web URL.';
 $lang['scratchpad_paths'] = 'Scratchpad files (one per line). Each file path must include the extension. Use a following A> line to set the pad name used in the wiki.';
 $lang['allow_in_comments'] = 'Whether to allow luxtools syntax (files/images/directory/scratchpad) to be used in comments.';