Refactor CSPMiddleware for extensibility (mozillaGH-36)

csp/contrib/rate_limiting.py

@@ -3,28 +3,20 @@
 from django.conf import settings
 
 from csp.middleware import CSPMiddleware
-from csp.utils import build_policy
 
 
 class RateLimitedCSPMiddleware(CSPMiddleware):
     """A CSP middleware that rate-limits the number of violation reports sent
     to report-uri by excluding it from some requests."""
 
-    def build_policy(self, request, response):
-        build_kwargs = {
-            key: getattr(response, '_csp_%s' % key, None)
-            for key in ('config', 'update', 'select')
-        }
-        replace = getattr(response, '_csp_replace', {})
-        nonce = getattr(request, '_csp_nonce', None)
+    def get_build_kwargs(self, request, response):
+        build_kwargs = super().get_build_kwargs(request, response)
+        replace = build_kwargs['replace'] or {}
 
         report_percentage = getattr(settings, 'CSP_REPORT_PERCENTAGE')
         include_report_uri = random.random() < report_percentage
         if not include_report_uri:
             replace['report-uri'] = None
+        build_kwargs['replace'] = replace
 
-        return build_policy(
-            replace=replace,
-            nonce=nonce,
-            **build_kwargs,
-        )
+        return build_kwargs

csp/middleware.py

@@ -75,12 +75,15 @@ def process_response(self, request, response):
             response[header] = ', '.join(policies)
         return response
 
-    def build_policy(self, request, response):
+    def get_build_kwargs(self, request, response):
         build_kwargs = {
             key: getattr(response, '_csp_%s' % key, None)
             for key in ('config', 'update', 'replace', 'select')
         }
+        build_kwargs["nonce"] = getattr(request, '_csp_nonce', None)
+        return build_kwargs
+
+    def build_policy(self, request, response):
         return build_policy(
-            nonce=getattr(request, '_csp_nonce', None),
-            **build_kwargs,
+            **self.get_build_kwargs(request, response),
         )