♻️(backend) replace Django permissions with feature flag decorator

Refactor feature flag mechanism from Django permission classes to custom
decorator that returns 404 Not Found when features are disabled instead
of exposing API structure through permission errors.

Improves security by preventing information disclosure about disabled
features and provides more appropriate response semantics. Custom
decorator approach is better suited for feature toggling than Django's
permission system which is designed for authorization.

src/backend/core/api/feature_flag.py

@@ -0,0 +1,45 @@
+"""Feature flag handler for the Meet core app."""
+
+from functools import wraps
+
+from django.conf import settings
+from django.http import Http404
+
+
+class FeatureFlag:
+    """Check if features are enabled and return error responses."""
+
+    FLAGS = {
+        "recording": "RECORDING_ENABLE",
+        "storage_event": "RECORDING_STORAGE_EVENT_ENABLE",
+        "subtitle": "ROOM_SUBTITLE_ENABLED",
+    }
+
+    @classmethod
+    def flag_is_active(cls, flag_name):
+        """Check if a feature flag is active."""
+
+        setting_name = cls.FLAGS.get(flag_name)
+
+        if setting_name is None:
+            return False
+
+        return getattr(settings, setting_name, False)
+
+    @classmethod
+    def require(cls, flag_name):
+        """Decorator to check feature at the beginning of endpoint methods."""
+
+        if flag_name not in cls.FLAGS:
+            raise ValueError(f"Unknown feature flag: {flag_name}")
+
+        def decorator(view_func):
+            @wraps(view_func)
+            def wrapper(self, request, *args, **kwargs):
+                if not cls.flag_is_active(flag_name):
+                    raise Http404
+                return view_func(self, request, *args, **kwargs)
+
+            return wrapper
+
+        return decorator

src/backend/core/api/permissions.py

@@ -1,7 +1,5 @@
 """Permission handlers for the Meet core app."""
 
-from django.conf import settings
-
 from rest_framework import permissions
 
 from ..models import RoleChoices
@@ -101,36 +99,6 @@ class HasPrivilegesOnRoom(IsAuthenticated):
         return obj.is_administrator_or_owner(request.user)
 
 
-class IsRecordingEnabled(permissions.BasePermission):
-    """Check if the recording feature is enabled."""
-
-    message = "Access denied, recording is disabled."
-
-    def has_permission(self, request, view):
-        """Determine if access is allowed based on settings."""
-        return settings.RECORDING_ENABLE
-
-
-class IsStorageEventEnabled(permissions.BasePermission):
-    """Check if the storage event feature is enabled."""
-
-    message = "Access denied, storage event is disabled."
-
-    def has_permission(self, request, view):
-        """Determine if access is allowed based on settings."""
-        return settings.RECORDING_STORAGE_EVENT_ENABLE
-
-
-class IsSubtitleEnabled(permissions.BasePermission):
-    """Check if the subtitle feature is enabled."""
-
-    message = "Access denied, subtitles are disabled."
-
-    def has_permission(self, request, view):
-        """Determine if access is allowed based on settings."""
-        return settings.ROOM_SUBTITLE_ENABLED
-
-
 class HasLiveKitRoomAccess(permissions.BasePermission):
     """Check if authenticated user's LiveKit token is for the specific room."""
 

src/backend/core/api/viewsets.py

@@ -59,6 +59,7 @@ from core.services.subtitle import SubtitleException, SubtitleService
 
 from ..authentication.livekit import LiveKitTokenAuthentication
 from . import permissions, serializers
+from .feature_flag import FeatureFlag
 
 # pylint: disable=too-many-ancestors
 
@@ -293,9 +294,9 @@ class RoomViewSet(
         url_path="start-recording",
         permission_classes=[
             permissions.HasPrivilegesOnRoom,
-            permissions.IsRecordingEnabled,
         ],
     )
+    @FeatureFlag.require("recording")
     def start_room_recording(self, request, pk=None):  # pylint: disable=unused-argument
         """Start recording a room."""
 
@@ -338,9 +339,9 @@ class RoomViewSet(
         url_path="stop-recording",
         permission_classes=[
             permissions.HasPrivilegesOnRoom,
-            permissions.IsRecordingEnabled,
         ],
     )
+    @FeatureFlag.require("recording")
     def stop_room_recording(self, request, pk=None):  # pylint: disable=unused-argument
         """Stop room recording."""
 
@@ -542,11 +543,11 @@ class RoomViewSet(
         methods=["post"],
         url_path="start-subtitle",
         permission_classes=[
-            permissions.IsSubtitleEnabled,
             permissions.HasLiveKitRoomAccess,
         ],
         authentication_classes=[LiveKitTokenAuthentication],
     )
+    @FeatureFlag.require("subtitle")
     def start_subtitle(self, request, pk=None):  # pylint: disable=unused-argument
         """Start realtime transcription for the room.
 
@@ -732,8 +733,8 @@ class RecordingViewSet(
         methods=["post"],
         url_path="storage-hook",
         authentication_classes=[StorageEventAuthentication],
-        permission_classes=[permissions.IsStorageEventEnabled],
     )
+    @FeatureFlag.require("storage_event")
     def on_storage_event_received(self, request, pk=None):  # pylint: disable=unused-argument
         """Handle incoming storage hook events for recordings."""