feat: add branded error pages

backend/workflows/error_views.py

@@ -0,0 +1,71 @@
+from django.shortcuts import render
+from django.utils.translation import gettext as _
+
+
+def _render_error(request, *, status: int, title: str, code: str, heading: str, message: str):
+    return render(
+        request,
+        'workflows/errors/error_page.html',
+        {
+            'error_title': title,
+            'error_code': code,
+            'error_heading': heading,
+            'error_message': message,
+        },
+        status=status,
+    )
+
+
+def bad_request(request, exception=None):
+    return _render_error(
+        request,
+        status=400,
+        title=_('Ungültige Anfrage'),
+        code='400',
+        heading=_('Die Anfrage konnte nicht verarbeitet werden'),
+        message=_('Die übermittelten Daten waren unvollständig oder ungültig. Bitte gehen Sie zurück und versuchen Sie es erneut.'),
+    )
+
+
+def permission_denied(request, exception=None):
+    return _render_error(
+        request,
+        status=403,
+        title=_('Kein Zugriff'),
+        code='403',
+        heading=_('Für diese Seite fehlt die Berechtigung'),
+        message=_('Sie sind angemeldet, aber für diesen Bereich nicht freigeschaltet. Wenn das nicht erwartet ist, wenden Sie sich an die Administration.'),
+    )
+
+
+def not_found(request, exception=None):
+    return _render_error(
+        request,
+        status=404,
+        title=_('Seite nicht gefunden'),
+        code='404',
+        heading=_('Diese Seite gibt es nicht'),
+        message=_('Die gewünschte Adresse ist nicht vorhanden oder wurde verschoben. Nutzen Sie die Startseite oder das Dashboard, um weiterzugehen.'),
+    )
+
+
+def server_error(request):
+    return _render_error(
+        request,
+        status=500,
+        title=_('Serverfehler'),
+        code='500',
+        heading=_('Etwas ist schiefgelaufen'),
+        message=_('Der Fehler wurde nicht sauber verarbeitet. Bitte laden Sie die Seite neu. Wenn das Problem bleibt, prüfen Sie die Server-Logs.'),
+    )
+
+
+def csrf_failure(request, reason=''):
+    return _render_error(
+        request,
+        status=400,
+        title=_('Sicherheitsprüfung fehlgeschlagen'),
+        code='400',
+        heading=_('Die Sitzung konnte nicht bestätigt werden'),
+        message=_('Bitte laden Sie die Seite neu und senden Sie das Formular erneut. Wenn das weiter passiert, prüfen Sie Host-, HTTPS- und CSRF-Einstellungen.'),
+    )

backend/workflows/middleware.py

@@ -5,17 +5,37 @@ from django.contrib import messages
 from django.contrib.auth import logout
 from django.contrib.messages.api import MessageFailure
 from django.core.cache import cache
-from django.http import HttpResponse
+from django.core.exceptions import PermissionDenied, SuspiciousOperation
+from django.http import Http404, HttpResponse
 from django.shortcuts import redirect, render
 from django.urls import reverse
 from django.utils import timezone
 from django.utils.translation import gettext as _
 
 from .branding import is_trial_expired, is_trial_mode_enabled
+from .error_views import bad_request, not_found, permission_denied, server_error
 from .logging_utils import clear_request_id, set_request_id
 from .roles import ROLE_PLATFORM_OWNER, get_user_role_key
 
 
+class FriendlyExceptionMiddleware:
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        if not settings.FORCE_BRANDED_ERROR_PAGES:
+            return self.get_response(request)
+
+        try:
+            return self.get_response(request)
+        except Http404 as exc:
+            return not_found(request, exc)
+        except PermissionDenied as exc:
+            return permission_denied(request, exc)
+        except SuspiciousOperation as exc:
+            return bad_request(request, exc)
+
+
 class RequestIDMiddleware:
     HEADER_NAME = 'X-Request-ID'
 

backend/workflows/templates/workflows/developer_handbook.html

@@ -185,9 +185,10 @@ docker compose exec -T web python manage.py check</code></pre>
       <ol>
         <li>Preserve behavior while refactoring.</li>
         <li>Prefer shared components over page-local special cases.</li>
-        <li>Do not overwrite environment-specific runtime config as a side effect of code deploys.</li>
-        <li>Keep code-driven behavior and data-driven behavior mentally separate.</li>
-        <li>Update documentation in the same branch when operational workflow changes.</li>
+      <li>Do not overwrite environment-specific runtime config as a side effect of code deploys.</li>
+      <li>Keep code-driven behavior and data-driven behavior mentally separate.</li>
+      <li>Update documentation in the same branch when operational workflow changes.</li>
+      <li>Keep branded error handling wired through the root URL handlers so production does not fall back to Django default error pages.</li>
       </ol>
     </div>
     <div class="box">
@@ -557,6 +558,9 @@ make backup-verify BACKUP_DIR=backups/backup_YYYYmmdd_HHMMSS</code></pre>
     <div class="note">
       The LAN test deployment intentionally uses <code>DJANGO_DEBUG=1</code> in <code>.env.test</code> because the security checks correctly reject insecure cookie settings when <code>DEBUG=0</code> and the deployment is still plain HTTP behind a local test topology. This is acceptable for the test box only. Production must run with HTTPS and <code>DEBUG=0</code>.
     </div>
+    <div class="note">
+      If you still want branded wrong-URL and permission pages on the LAN test server while keeping <code>DJANGO_DEBUG=1</code>, enable <code>FORCE_BRANDED_ERROR_PAGES=1</code> in <code>.env.test</code>. Full branded <code>500</code> behavior still requires <code>DEBUG=0</code>, which remains the correct production-style setup.
+    </div>
 
     <h2 id="deploy">18) Deployment</h2>
     <h3>Test server stack</h3>

backend/workflows/templates/workflows/errors/error_page.html

@@ -0,0 +1,31 @@
+{% extends 'workflows/base_shell.html' %}
+{% load i18n %}
+
+{% block title %}{{ error_title }}{% endblock %}
+
+{% block shell_body %}
+  {% include 'workflows/includes/app_header.html' with header_show_home=1 header_inside_shell=1 %}
+  <div class="page-stack">
+    <section class="surface-card" style="max-width: 760px; margin: 0 auto;">
+      <div class="surface-head">
+        <div>
+          <div class="eyebrow">{% trans "Fehlerseite" %}</div>
+          <h1>{{ error_heading }}</h1>
+          <p class="sub">{{ error_message }}</p>
+        </div>
+        <div class="app-stat-card" style="min-width: 120px; text-align: center;">
+          <strong style="font-size: 2rem; line-height: 1;">{{ error_code }}</strong>
+          <span>{% trans "Status" %}</span>
+        </div>
+      </div>
+      <div class="app-action-row">
+        <a class="btn btn-primary" href="/">{% trans "Zur Startseite" %}</a>
+        {% if request.user.is_authenticated %}
+        <a class="btn btn-secondary" href="/requests/">{% trans "Zum Dashboard" %}</a>
+        {% else %}
+        <a class="btn btn-secondary" href="/accounts/login/">{% trans "Anmelden" %}</a>
+        {% endif %}
+      </div>
+    </section>
+  </div>
+{% endblock %}

backend/workflows/tests/error_test_urls.py

@@ -0,0 +1,28 @@
+from django.core.exceptions import PermissionDenied
+from django.http import HttpResponse
+from django.urls import include, path
+
+
+def ok_view(request):
+    return HttpResponse('ok')
+
+
+def deny_view(request):
+    raise PermissionDenied('forbidden')
+
+
+def explode_view(request):
+    raise RuntimeError('boom')
+
+
+handler400 = 'workflows.error_views.bad_request'
+handler403 = 'workflows.error_views.permission_denied'
+handler404 = 'workflows.error_views.not_found'
+handler500 = 'workflows.error_views.server_error'
+
+urlpatterns = [
+    path('healthz/', ok_view, name='healthz'),
+    path('raise-403/', deny_view, name='raise_403'),
+    path('raise-500/', explode_view, name='raise_500'),
+    path('', include('workflows.urls')),
+]

backend/workflows/tests/test_error_pages.py

@@ -0,0 +1,62 @@
+from django.test import Client, RequestFactory, TestCase, override_settings
+
+from workflows.error_views import csrf_failure
+
+
+@override_settings(
+    DEBUG=False,
+    ROOT_URLCONF='workflows.tests.error_test_urls',
+    ALLOWED_HOSTS=['testserver'],
+)
+class ErrorPageTests(TestCase):
+    def setUp(self):
+        self.client = Client()
+        self.client.raise_request_exception = False
+
+    def test_custom_404_page_is_rendered(self):
+        response = self.client.get('/missing-page/')
+
+        self.assertEqual(response.status_code, 404)
+        self.assertTemplateUsed(response, 'workflows/errors/error_page.html')
+        self.assertContains(response, '404', status_code=404)
+
+    def test_custom_403_page_is_rendered(self):
+        response = self.client.get('/raise-403/')
+
+        self.assertEqual(response.status_code, 403)
+        self.assertTemplateUsed(response, 'workflows/errors/error_page.html')
+        self.assertContains(response, '403', status_code=403)
+
+    def test_custom_500_page_is_rendered(self):
+        response = self.client.get('/raise-500/')
+
+        self.assertEqual(response.status_code, 500)
+        self.assertTemplateUsed(response, 'workflows/errors/error_page.html')
+        self.assertContains(response, '500', status_code=500)
+
+    def test_csrf_failure_view_uses_custom_400_page(self):
+        request = RequestFactory().post('/test/')
+
+        response = csrf_failure(request)
+
+        self.assertEqual(response.status_code, 400)
+        self.assertContains(response, '400', status_code=400)
+
+
+@override_settings(
+    DEBUG=True,
+    FORCE_BRANDED_ERROR_PAGES=True,
+    ROOT_URLCONF='workflows.tests.error_test_urls',
+    ALLOWED_HOSTS=['testserver'],
+)
+class ForcedBrandedErrorPageTests(TestCase):
+    def setUp(self):
+        self.client = Client()
+        self.client.raise_request_exception = False
+
+    def test_missing_url_uses_branded_404_even_with_debug_enabled(self):
+        response = self.client.get('/missing-page/')
+
+        self.assertEqual(response.status_code, 404)
+        self.assertTemplateUsed(response, 'workflows/errors/error_page.html')
+        self.assertContains(response, '404', status_code=404)

backend/workflows/urls.py

@@ -1,6 +1,6 @@
-from django.urls import path
+from django.urls import path, re_path
 
-from . import views
+from . import error_views, views
 
 urlpatterns = [
     path('healthz/', views.healthz, name='healthz'),
@@ -65,4 +65,5 @@ urlpatterns = [
     path('requests/delete/<str:kind>/<int:request_id>/', views.delete_request_from_dashboard, name='delete_request_from_dashboard'),
     path('requests/retry/<str:kind>/<int:request_id>/', views.retry_request_from_dashboard, name='retry_request_from_dashboard'),
     path('requests/timeline/<str:kind>/<int:request_id>/', views.request_timeline_page, name='request_timeline_page'),
+    re_path(r'^.*$', error_views.not_found, name='not_found_fallback'),
 ]