diff --git a/keepmenu/__init__.py b/keepmenu/__init__.py
index 554d636..dc64463 100644
--- a/keepmenu/__init__.py
+++ b/keepmenu/__init__.py
@@ -8,7 +8,8 @@
 import shlex
 from subprocess import run, DEVNULL
 import sys
-from os.path import exists, expanduser
+import tempfile
+from os.path import exists, expanduser, join
 
 from keepmenu.menu import dmenu_err
 
@@ -22,7 +23,29 @@
 # file_handler.setFormatter(formatter)
 # logger.addHandler(file_handler)
 
-AUTH_FILE = expanduser("~/.cache/.keepmenu-auth")
+
+def get_runtime_dir():
+    """Get the runtime directory for auth file storage.
+
+    Prefers $XDG_RUNTIME_DIR/keepmenu/ for security (tmpfs-backed, auto-cleanup
+    on logout, proper permissions enforced by systemd). Falls back to
+    $TMPDIR/keepmenu-<uid>/ which is also typically tmpfs and cleared on reboot.
+
+    Returns: str path to runtime directory
+
+    """
+    xdg_runtime = os.environ.get('XDG_RUNTIME_DIR')
+    if xdg_runtime and exists(xdg_runtime):
+        runtime_dir = join(xdg_runtime, 'keepmenu')
+    else:
+        runtime_dir = join(tempfile.gettempdir(), f'keepmenu-{os.getuid()}')
+    # Ensure directory exists with secure permissions
+    if not exists(runtime_dir):
+        os.makedirs(runtime_dir, mode=0o700)
+    return runtime_dir
+
+
+AUTH_FILE = join(get_runtime_dir(), ".keepmenu-auth")
 CONF_FILE = expanduser("~/.config/keepmenu/config.ini")
 SECRET_VALID_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
 
diff --git a/keepmenu/__main__.py b/keepmenu/__main__.py
index 8887755..9593b20 100644
--- a/keepmenu/__main__.py
+++ b/keepmenu/__main__.py
@@ -41,7 +41,10 @@ def port_in_use(port):
         return s.connect_ex(('127.0.0.1', port)) == 0
 
 def get_auth():
-    """Generate and save port and authkey to ~/.cache/.keepmenu-auth
+    """Generate and save port and authkey to runtime directory.
+
+    Uses $XDG_RUNTIME_DIR/keepmenu/ if available (tmpfs-backed, auto-cleanup),
+    otherwise falls back to $TMPDIR/keepmenu-<uid>/.
 
     Returns: int port, bytestring authkey
 
diff --git a/tests/tests.py b/tests/tests.py
index eedb8a0..705d2ac 100644
--- a/tests/tests.py
+++ b/tests/tests.py
@@ -19,6 +19,78 @@
 SECRET2 = 'PW4YAYYZVDE5RK2AOLKUATNZIKAFQLZO'
 
 
+class TestRuntimeDir(unittest.TestCase):
+    """Test get_runtime_dir() function for auth file location
+
+    """
+    def setUp(self):
+        self.tmpdir = tempfile.mkdtemp()
+        # Save original environment and tempfile cache
+        self.orig_xdg_runtime = os.environ.get('XDG_RUNTIME_DIR')
+        self.orig_tmpdir = os.environ.get('TMPDIR')
+        self.orig_tempfile_tempdir = tempfile.tempdir
+
+    def tearDown(self):
+        rmtree(self.tmpdir)
+        # Restore original environment
+        if self.orig_xdg_runtime is not None:
+            os.environ['XDG_RUNTIME_DIR'] = self.orig_xdg_runtime
+        elif 'XDG_RUNTIME_DIR' in os.environ:
+            del os.environ['XDG_RUNTIME_DIR']
+        if self.orig_tmpdir is not None:
+            os.environ['TMPDIR'] = self.orig_tmpdir
+        elif 'TMPDIR' in os.environ:
+            del os.environ['TMPDIR']
+        # Restore tempfile cache
+        tempfile.tempdir = self.orig_tempfile_tempdir
+
+    def test_xdg_runtime_dir_used_when_set(self):
+        """Test that $XDG_RUNTIME_DIR/keepmenu/ is used when available
+        """
+        xdg_runtime = os.path.join(self.tmpdir, 'runtime')
+        os.makedirs(xdg_runtime, mode=0o700)
+        os.environ['XDG_RUNTIME_DIR'] = xdg_runtime
+
+        runtime_dir = KM.get_runtime_dir()
+
+        self.assertEqual(runtime_dir, os.path.join(xdg_runtime, 'keepmenu'))
+        self.assertTrue(os.path.exists(runtime_dir))
+        self.assertEqual(os.stat(runtime_dir).st_mode & 0o777, 0o700)
+
+    def test_tmpdir_fallback_when_xdg_runtime_unset(self):
+        """Test fallback to $TMPDIR/keepmenu-<uid>/ when XDG_RUNTIME_DIR not set
+        """
+        if 'XDG_RUNTIME_DIR' in os.environ:
+            del os.environ['XDG_RUNTIME_DIR']
+        custom_tmpdir = os.path.join(self.tmpdir, 'tmp')
+        os.makedirs(custom_tmpdir, mode=0o777)
+        os.environ['TMPDIR'] = custom_tmpdir
+        # Reset tempfile cache so it picks up new TMPDIR
+        tempfile.tempdir = None
+
+        runtime_dir = KM.get_runtime_dir()
+
+        expected = os.path.join(custom_tmpdir, f'keepmenu-{os.getuid()}')
+        self.assertEqual(runtime_dir, expected)
+        self.assertTrue(os.path.exists(runtime_dir))
+        self.assertEqual(os.stat(runtime_dir).st_mode & 0o777, 0o700)
+
+    def test_tmpdir_fallback_when_xdg_runtime_dir_not_exists(self):
+        """Test fallback when XDG_RUNTIME_DIR is set but doesn't exist
+        """
+        os.environ['XDG_RUNTIME_DIR'] = '/nonexistent/path'
+        custom_tmpdir = os.path.join(self.tmpdir, 'tmp')
+        os.makedirs(custom_tmpdir, mode=0o777)
+        os.environ['TMPDIR'] = custom_tmpdir
+        # Reset tempfile cache so it picks up new TMPDIR
+        tempfile.tempdir = None
+
+        runtime_dir = KM.get_runtime_dir()
+
+        expected = os.path.join(custom_tmpdir, f'keepmenu-{os.getuid()}')
+        self.assertEqual(runtime_dir, expected)
+
+
 class TestServer(unittest.TestCase):
     """Test various BaseManager server functions