Security: Improve overall security in a few ways (#12501)

- Make sure we're always using regex with timeouts for user controlled data
- Adds rate limiting to the token endpoint (configurable)
- Signs the classifier pickle file with the SECRET_KEY and refuse to load one which doesn't verify.
- Require the user to set a secret key, instead of falling back to our old hard coded one

src/paperless/views.py

@@ -34,6 +34,7 @@ from rest_framework.pagination import PageNumberPagination
 from rest_framework.permissions import DjangoModelPermissions
 from rest_framework.permissions import IsAuthenticated
 from rest_framework.response import Response
+from rest_framework.throttling import ScopedRateThrottle
 from rest_framework.viewsets import ModelViewSet
 
 from documents.permissions import PaperlessObjectPermissions
@@ -51,6 +52,8 @@ from paperless_ai.indexing import vector_store_file_exists
 
 class PaperlessObtainAuthTokenView(ObtainAuthToken):
     serializer_class = PaperlessAuthTokenSerializer
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "login"
 
 
 class StandardPagination(PageNumberPagination):