fix(course): base URL from request and default path

Use request.build_absolute_uri('/') to derive the base domain instead
of relying on ONLINE_CLASS_FRONTEND_DOMAIN/SITE_DOMAIN. This produces
correct entry URLs based on the incoming request.

Add ONLINE_CLASS_DEFAULT_PATH (default: 'join-class') as a fallback
when redirect_path is not provided.

Update the view to pass request to _build_base_url.

apps/course/views/course.py

@@ -324,17 +324,20 @@ class CourseOnlineClassTokenAPIView(GenericAPIView):
         user_token, _ = Token.objects.get_or_create(user=request.user)
         identifier = f"{request.user.id}:{user_token.key[:8]}"
         token = manager.generate_token(course_id=course.id, user_identifier=identifier)
+
+        redirect_path = serializer.validated_data.get('redirect_path')
+        base_url, path_value = self._build_base_components(request, redirect_path)
+
         manager.store_token(token, {
             'course_id': course.id,
             'user_id': request.user.id,
             'user_token': user_token.key,
+            'redirect_path': path_value,
             'extra': {
                 'professor_in_class': False,
             },
         })
 
-        redirect_path = serializer.validated_data.get('redirect_path')
-        base_url = self._build_base_url(request, redirect_path)
         entry_url = manager.build_entry_url(token, base_url=base_url)
 
         return Response({
@@ -343,13 +346,15 @@ class CourseOnlineClassTokenAPIView(GenericAPIView):
             'expires_in': getattr(settings, 'ONLINE_CLASS_TOKEN_TTL', 300),
         }, status=status.HTTP_201_CREATED)
 
-    def _build_base_url(self, request, redirect_path=None) -> str:
+    def _build_base_components(self, request, redirect_path=None):
         base_uri = request.build_absolute_uri('/')
         domain = base_uri.rstrip('/')
         default_path = getattr(settings, 'ONLINE_CLASS_DEFAULT_PATH', 'join-class')
         target_path = redirect_path or default_path
         sanitized = str(target_path).strip('/')
-        return f"{domain}/{sanitized}" if sanitized else domain
+        path_value = f"/{sanitized}" if sanitized else '/'
+        base_url = f"{domain}/{sanitized}" if sanitized else domain
+        return base_url, path_value
 
     @staticmethod
     def _user_has_access(user, course: Course) -> bool:
@@ -426,6 +431,7 @@ class CourseOnlineClassTokenValidateAPIView(GenericAPIView):
             'scheduled_times': timing_data,
             'generated_at': payload.get('generated_at'),
             'validated_at': timezone.now().isoformat(),
+            'redirect_path': payload.get('redirect_path'),
         }
         metadata.update(self._resolve_live_session_timings(course, payload))
         return metadata