feat(websockets): Authenticate with signed tokens.

Authentication is now done using a signed token provided by the Django
server, sent by the JS client and checked by the WebSocket server.

The token contains a `permissions` key that's checked to ensure the user
has access to the map "room", where events will be shared by the peers.

pyproject.toml

@@ -32,7 +32,6 @@ dependencies = [
   "django-agnocomplete==2.2.0",
   "django-environ==0.11.2",
   "django-probes==1.7.0",
-  "django-sesame==3.2.2",
   "Pillow==10.3.0",
   "psycopg==3.1.19",
   "pydantic==2.7.0",

umap/settings/base.py

@@ -289,11 +289,6 @@ if SOCIAL_AUTH_OPENSTREETMAP_OAUTH2_KEY and SOCIAL_AUTH_OPENSTREETMAP_OAUTH2_SEC
 
 AUTHENTICATION_BACKENDS += ("django.contrib.auth.backends.ModelBackend",)
 
-# Websockets configuration
-AUTHENTICATION_BACKENDS += ("sesame.backends.ModelBackend",)
-
-SESAME_MAX_AGE = 30
-
 LOGGING = {
     "version": 1,
     "disable_existing_loggers": False,

umap/urls.py

@@ -155,6 +155,11 @@ map_urls = [
         views.UpdateDataLayerPermissions.as_view(),
         name="datalayer_permissions",
     ),
+    path(
+        "map/<int:map_id>/ws-token/",
+        views.get_websocket_auth_token,
+        name="map_websocket_auth_token",
+    ),
 ]
 if settings.DEFAULT_FROM_EMAIL:
     map_urls.append(

umap/views.py

@@ -24,7 +24,7 @@ from django.contrib.staticfiles.storage import staticfiles_storage
 from django.core.exceptions import PermissionDenied
 from django.core.mail import send_mail
 from django.core.paginator import EmptyPage, PageNotAnInteger, Paginator
-from django.core.signing import BadSignature, Signer
+from django.core.signing import BadSignature, Signer, TimestampSigner
 from django.core.validators import URLValidator, ValidationError
 from django.http import (
     Http404,
@@ -40,7 +40,6 @@ from django.shortcuts import get_object_or_404
 from django.urls import resolve, reverse, reverse_lazy
 from django.utils import translation
 from django.utils.encoding import smart_bytes
-from django.utils.http import http_date
 from django.utils.timezone import make_aware
 from django.utils.translation import gettext as _
 from django.views.decorators.cache import cache_control
@@ -327,9 +326,9 @@ class UserDownload(DetailView, SearchMixin):
                 zip_file.writestr(file_name, geojson_file.getvalue())
 
         response = HttpResponse(zip_buffer.getvalue(), content_type="application/zip")
-        response["Content-Disposition"] = (
-            'attachment; filename="umap_backup_complete.zip"'
-        )
+        response[
+            "Content-Disposition"
+        ] = 'attachment; filename="umap_backup_complete.zip"'
         return response
 
 
@@ -675,9 +674,9 @@ class MapDownload(DetailView):
     def render_to_response(self, context, *args, **kwargs):
         umapjson = self.object.generate_umapjson(self.request)
         response = simple_json_response(**umapjson)
-        response["Content-Disposition"] = (
-            f'attachment; filename="umap_backup_{self.object.slug}.umap"'
-        )
+        response[
+            "Content-Disposition"
+        ] = f'attachment; filename="umap_backup_{self.object.slug}.umap"'
         return response
 
 
@@ -778,6 +777,36 @@ class MapCreate(FormLessEditMixin, PermissionsMixin, CreateView):
         return response
 
 
+def get_websocket_auth_token(request, map_id, map_inst):
+    """Return an signed authentication token for the currently
+    connected user, allowing edits for this map over WebSocket.
+
+    If the user is anonymous, return a signed token with the map id.
+
+    The returned token is a signed object with the following keys:
+    - user: user primary key OR "anonymous"
+    - map_id: the map id
+    - permissions: a list of allowed permissions for this user and this map
+    """
+    map_object: Map = Map.objects.get(pk=map_id)
+
+    if map_object.can_edit(request.user, request):
+        permissions = ["edit"]
+        if map_object.can_delete(request.user, request):
+            permissions.append("owner")
+
+        if request.user.is_authenticated:
+            user = request.user.pk
+        else:
+            user = "anonymous"
+        signed_token = TimestampSigner().sign_object(
+            {"user": user, "map_id": map_id, "permissions": permissions}
+        )
+        return simple_json_response(token=signed_token)
+    else:
+        return HttpResponseForbidden
+
+
 class MapUpdate(FormLessEditMixin, PermissionsMixin, UpdateView):
     model = Map
     form_class = MapSettingsForm

umap/ws.py

@@ -7,8 +7,9 @@ from typing import Literal
 import django
 import websockets
 from django.conf import settings
+from django.core.signing import TimestampSigner
 from pydantic import BaseModel
-from pydantic.types import UUID4
+from websockets import WebSocketClientProtocol
 from websockets.server import serve
 
 # This needs to run before the django-specific imports
@@ -29,7 +30,6 @@ CONNECTIONS = defaultdict(set)
 class JoinMessage(BaseModel):
     kind: str = "join"
     token: str
-    map_id: UUID4
 
 
 class OperationMessage(BaseModel):
@@ -39,11 +39,15 @@ class OperationMessage(BaseModel):
     data: dict
 
 
-async def join_and_listen(map_id, websocket):
+async def join_and_listen(
+    map_id: int, permissions: list, user: str | int, websocket: WebSocketClientProtocol
+):
     """Join a "room" whith other connected peers.
 
     New messages will be broadcasted to other connected peers.
     """
+    print(f"{user} joined room #{map_id}")
+    # FIXME: Persist permissions and user info.
     CONNECTIONS[map_id].add(websocket)
     try:
         async for raw_message in websocket:
@@ -67,12 +71,13 @@ async def handler(websocket):
 
     # The first event should always be 'join'
     message: JoinMessage = JoinMessage.model_validate_json(raw_message)
+    signed = TimestampSigner().unsign_object(message.token, max_age=30)
+    user, map_id, permissions = signed.values()
 
-    user: User = await asyncio.to_thread(get_user, message.token)
-    map_obj: Map = await asyncio.to_thread(Map.objects.get, message.map_id)
-
-    if map_obj.can_edit(user):
-        await join_and_listen(message.map_id, websocket)
+    # We trust the signed info from the server to give access
+    # If the user can edit the map, let her in
+    if "edit" in signed["permissions"]:
+        await join_and_listen(map_id, permissions, user, websocket)
 
 
 async def main():