diff --git a/backend/workflows/context_processors.py b/backend/workflows/context_processors.py
index 6fac856..450bd35 100644
--- a/backend/workflows/context_processors.py
+++ b/backend/workflows/context_processors.py
@@ -19,5 +19,12 @@ def role_context(request):
         )
     else:
         context.update({'header_notifications': [], 'header_unread_notification_count': 0})
-    context.update({'static_asset_version': settings.STATIC_ASSET_VERSION})
+    context.update(
+        {
+            'static_asset_version': settings.STATIC_ASSET_VERSION,
+            'session_idle_timeout_seconds': settings.SESSION_IDLE_TIMEOUT_SECONDS,
+            'session_reauth_timeout_seconds': settings.SENSITIVE_ACTION_REAUTH_SECONDS,
+            'force_branded_error_pages': settings.FORCE_BRANDED_ERROR_PAGES,
+        }
+    )
     return context
diff --git a/backend/workflows/middleware.py b/backend/workflows/middleware.py
index 65e2f64..367a4ca 100644
--- a/backend/workflows/middleware.py
+++ b/backend/workflows/middleware.py
@@ -127,6 +127,7 @@ class RateLimitMiddleware:
 class AuthSessionHardeningMiddleware:
     EXEMPT_PREFIXES = (
         '/healthz/',
+        '/session/keepalive/',
         '/i18n/',
         '/accounts/login/',
         '/accounts/logout/',
diff --git a/backend/workflows/static/workflows/js/session_warning.js b/backend/workflows/static/workflows/js/session_warning.js
new file mode 100644
index 0000000..736acd4
--- /dev/null
+++ b/backend/workflows/static/workflows/js/session_warning.js
@@ -0,0 +1,82 @@
+(function () {
+  const config = window.WorkdockSessionConfig;
+  if (!config || !config.idleTimeoutSeconds) return;
+
+  const warningLeadSeconds = Math.min(300, Math.max(60, Math.floor(config.idleTimeoutSeconds / 6)));
+  const modal = document.getElementById("app-session-warning-modal");
+  const countdown = document.getElementById("app-session-warning-countdown");
+  const extendButton = document.getElementById("app-session-warning-extend");
+  if (!modal || !countdown || !extendButton) return;
+
+  let lastConfirmedAt = Date.now();
+  let warningVisible = false;
+  let keepaliveInFlight = false;
+
+  function getCsrfToken() {
+    const cookie = document.cookie
+      .split(";")
+      .map((item) => item.trim())
+      .find((item) => item.startsWith("csrftoken="));
+    return cookie ? decodeURIComponent(cookie.split("=")[1]) : "";
+  }
+
+  function hideWarning() {
+    if (!warningVisible) return;
+    modal.hidden = true;
+    modal.setAttribute("aria-hidden", "true");
+    warningVisible = false;
+  }
+
+  function showWarning(secondsLeft) {
+    countdown.textContent = `Noch etwa ${secondsLeft} Sekunden bis zur automatischen Abmeldung.`;
+    if (warningVisible) return;
+    modal.hidden = false;
+    modal.setAttribute("aria-hidden", "false");
+    warningVisible = true;
+  }
+
+  async function sendKeepalive() {
+    if (keepaliveInFlight) return;
+    keepaliveInFlight = true;
+    try {
+      const response = await fetch(config.keepaliveUrl, {
+        method: "POST",
+        headers: {
+          "Content-Type": "application/json",
+          "X-CSRFToken": getCsrfToken(),
+          "X-Requested-With": "XMLHttpRequest",
+        },
+        credentials: "same-origin",
+        body: JSON.stringify({ keepalive: true }),
+      });
+      if (!response.ok) {
+        window.location.href = config.loginUrl;
+        return;
+      }
+      lastConfirmedAt = Date.now();
+      hideWarning();
+    } catch (_error) {
+      window.location.href = config.loginUrl;
+    } finally {
+      keepaliveInFlight = false;
+    }
+  }
+
+  function tick() {
+    const elapsedSeconds = Math.floor((Date.now() - lastConfirmedAt) / 1000);
+    const secondsLeft = config.idleTimeoutSeconds - elapsedSeconds;
+    if (secondsLeft <= 0) {
+      window.location.href = config.loginUrl;
+      return;
+    }
+    if (secondsLeft <= warningLeadSeconds) {
+      showWarning(secondsLeft);
+    }
+  }
+
+  extendButton.addEventListener("click", function () {
+    sendKeepalive();
+  });
+
+  setInterval(tick, 1000);
+})();
diff --git a/backend/workflows/templates/workflows/base_shell.html b/backend/workflows/templates/workflows/base_shell.html
index 54e2e6b..8d4bf40 100644
--- a/backend/workflows/templates/workflows/base_shell.html
+++ b/backend/workflows/templates/workflows/base_shell.html
@@ -14,6 +14,16 @@
   {% block extra_head %}{% endblock %}
 </head>
 <body{% block body_attrs %}{% endblock %}>
+  {% if request.user.is_authenticated %}
+  <script>
+    window.WorkdockSessionConfig = {
+      idleTimeoutSeconds: {{ session_idle_timeout_seconds|default:0 }},
+      reauthTimeoutSeconds: {{ session_reauth_timeout_seconds|default:0 }},
+      keepaliveUrl: "/session/keepalive/",
+      loginUrl: "/accounts/login/"
+    };
+  </script>
+  {% endif %}
   {% block pre_shell %}{% endblock %}
   {% if portal_trial_enabled %}
   <div class="app-trial-banner{% if portal_trial_expired %} is-expired{% endif %}">
@@ -93,8 +103,29 @@
       </div>
     </div>
   </div>
+  <div class="confirm-modal" id="app-session-warning-modal" hidden aria-hidden="true">
+    <div class="confirm-backdrop"></div>
+    <div class="confirm-dialog" role="dialog" aria-modal="true" aria-labelledby="app-session-warning-title" aria-describedby="app-session-warning-copy">
+      <div class="confirm-dialog-head">
+        <p class="action-progress-kicker">{% trans "Sitzung" %}</p>
+        <h2 id="app-session-warning-title">{% trans "Ihre Sitzung läuft bald ab" %}</h2>
+      </div>
+      <p class="confirm-message" id="app-session-warning-copy">
+        {% trans "Sie sind weiterhin angemeldet, aber diese Sitzung wird bald ablaufen. Bleiben Sie aktiv, wenn Sie weiterarbeiten möchten." %}
+      </p>
+      <p class="confirm-message" id="app-session-warning-countdown"></p>
+      <div class="confirm-actions">
+        <form method="post" action="{% url 'logout' %}">
+          {% csrf_token %}
+          <button class="btn btn-secondary" type="submit">{% trans "Abmelden" %}</button>
+        </form>
+        <button class="btn btn-primary" type="button" id="app-session-warning-extend">{% trans "Angemeldet bleiben" %}</button>
+      </div>
+    </div>
+  </div>
   <script src="{% static 'workflows/js/confirm_dialog.js' %}?v={{ static_asset_version }}"></script>
   <script src="{% static 'workflows/js/action_progress.js' %}?v={{ static_asset_version }}"></script>
+  <script src="{% static 'workflows/js/session_warning.js' %}?v={{ static_asset_version }}"></script>
   {% block extra_scripts %}{% endblock %}
 </body>
 </html>
diff --git a/backend/workflows/tests/test_session_warning.py b/backend/workflows/tests/test_session_warning.py
new file mode 100644
index 0000000..706fa3c
--- /dev/null
+++ b/backend/workflows/tests/test_session_warning.py
@@ -0,0 +1,49 @@
+from django.contrib.auth import get_user_model
+from django.test import Client, TestCase
+from django.test.utils import override_settings
+
+
+TEST_STORAGES = {
+    'default': {
+        'BACKEND': 'django.core.files.storage.FileSystemStorage',
+    },
+    'staticfiles': {
+        'BACKEND': 'django.contrib.staticfiles.storage.StaticFilesStorage',
+    },
+}
+
+
+@override_settings(STORAGES=TEST_STORAGES)
+class SessionWarningTests(TestCase):
+    def setUp(self):
+        self.user = get_user_model().objects.create_user(
+            username='session-user',
+            email='session@example.com',
+            password='secret-12345',
+        )
+
+    def test_base_shell_exposes_session_warning_config(self):
+        client = Client(HTTP_HOST='localhost')
+        client.force_login(self.user)
+
+        response = client.get('/')
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, 'WorkdockSessionConfig')
+        self.assertContains(response, '/session/keepalive/')
+        self.assertContains(response, 'Ihre Sitzung läuft bald ab')
+
+    def test_keepalive_refreshes_session_timestamps(self):
+        client = Client(HTTP_HOST='localhost')
+        client.force_login(self.user)
+        session = client.session
+        session['last_activity_ts'] = 1
+        session['auth_fresh_ts'] = 1
+        session.save()
+
+        response = client.post('/session/keepalive/', {}, HTTP_HOST='localhost')
+
+        self.assertEqual(response.status_code, 200)
+        session = client.session
+        self.assertGreater(session['last_activity_ts'], 1)
+        self.assertGreater(session['auth_fresh_ts'], 1)
diff --git a/backend/workflows/urls.py b/backend/workflows/urls.py
index 7971322..5650f2e 100644
--- a/backend/workflows/urls.py
+++ b/backend/workflows/urls.py
@@ -4,6 +4,7 @@ from . import error_views, views
 
 urlpatterns = [
     path('healthz/', views.healthz, name='healthz'),
+    path('session/keepalive/', views.session_keepalive, name='session_keepalive'),
     path('', views.home, name='home'),
     path('account/', views.account_profile_page, name='account_profile_page'),
     path('notifications/<int:notification_id>/read/', views.mark_notification_read, name='mark_notification_read'),
diff --git a/backend/workflows/views.py b/backend/workflows/views.py
index 3b4efaa..02997a9 100644
--- a/backend/workflows/views.py
+++ b/backend/workflows/views.py
@@ -138,6 +138,22 @@ def mark_all_notifications_read(request):
     UserNotification.objects.filter(user=request.user, read_at__isnull=True).update(read_at=timezone.now())
     return _redirect_back(request, 'home')
 
+
+@login_required
+@require_POST
+def session_keepalive(request):
+    now_ts = int(timezone.now().timestamp())
+    request.session['last_activity_ts'] = now_ts
+    request.session['auth_fresh_ts'] = now_ts
+    return JsonResponse(
+        {
+            'status': 'ok',
+            'idle_timeout_seconds': settings.SESSION_IDLE_TIMEOUT_SECONDS,
+            'reauth_timeout_seconds': settings.SENSITIVE_ACTION_REAUTH_SECONDS,
+            'refreshed_at': now_ts,
+        }
+    )
+
 def healthz(request):
     db_ok = True
     try: