MPP-3838: restore safer CSP

Use a new EagerNonceCSPMiddleware to add nonce to the CSP and update the
React app to include it in dynamic scripts.

frontend/src/components/layout/Layout.tsx

@@ -34,6 +34,7 @@ import { HolidayPromoBanner } from "./topmessage/HolidayPromoBanner";
 import { isFlagActive } from "../../functions/waffle";
 import { useMetrics } from "../../hooks/metrics";
 import { GoogleAnalyticsWorkaround } from "../GoogleAnalyticsWorkaround";
+import { getCookie } from "../../functions/cookies";
 
 export type Props = {
   children: ReactNode;
@@ -293,6 +294,7 @@ export const Layout = (props: Props) => {
       metricsEnabled === "enabled" ? (
         <GoogleAnalyticsWorkaround
           gaId={props.runtimeData.GA4_MEASUREMENT_ID}
+          nonce={getCookie("csp_nonce")}
           debugMode={
             process.env.NEXT_PUBLIC_GA4_DEBUG_MODE === "true" &&
             process.env.NODE_ENV !== "test"

privaterelay/middleware.py

@@ -1,3 +1,5 @@
+import binascii
+import os
 import re
 import time
 from collections.abc import Callable
@@ -8,11 +10,61 @@ from django.http import HttpRequest, HttpResponse
 from django.shortcuts import redirect
 
 import markus
+from csp.middleware import CSPMiddleware
 from whitenoise.middleware import WhiteNoiseMiddleware
 
 metrics = markus.get_metrics("fx-private-relay")
 
 
+# To find all the URL paths that serve HTML which need the CSP nonce:
+# python manage.py collectstatic
+# find staticfiles -type f -name 'index.html'
+CSP_NONCE_COOKIE_PATHS = [
+    "/",
+    "/contains-tracker-warning",
+    "/flags",
+    "/faq",
+    "/vpn-relay/waitlist",
+    "/accounts/settings",
+    "/accounts/profile",
+    "/accounts/account_inactive",
+    "/vpn-relay-welcome",
+    "/phone/waitlist",
+    "/phone",
+    "/404",
+    "/tracker-report",
+    "/premium/waitlist",
+    "/premium",
+]
+
+
+class EagerNonceCSPMiddleware(CSPMiddleware):
+    # We need a nonce to use Google Tag Manager with a safe CSP:
+    # https://developers.google.com/tag-platform/security/guides/csp
+    # django-csp only includes the nonce value in the CSP header if the csp_nonce
+    # attribute is accessed:
+    # https://django-csp.readthedocs.io/en/latest/nonce.html
+    # That works for urls served by Django views that access the attribute but it
+    # doesn't work for urls that are served by views which don't access the attribute.
+    # (e.g., Whitenoise)
+    # So, to ensure django-csp includes the nonce value in the CSP header of every
+    # response, we override the default CSPMiddleware with this middleware. If the
+    # request is for one of the HTML urls, this middleware sets the request.csp_nonce
+    # attribute and adds a cookie for the React app to get the nonce value for scripts.
+    def process_request(self, request):
+        if request.path in CSP_NONCE_COOKIE_PATHS:
+            request_nonce = binascii.hexlify(os.urandom(16)).decode("ascii")
+            request._csp_nonce = request_nonce
+
+    def process_response(self, request, response):
+        response = super().process_response(request, response)
+        if request.path in CSP_NONCE_COOKIE_PATHS:
+            response.set_cookie(
+                "csp_nonce", request._csp_nonce, secure=True, samesite="Strict"
+            )
+        return response
+
+
 class RedirectRootIfLoggedIn:
     def __init__(self, get_response):
         self.get_response = get_response

privaterelay/settings.py

@@ -26,7 +26,7 @@ import dj_database_url
 import django_stubs_ext
 import markus
 import sentry_sdk
-from csp.constants import NONE, SELF, UNSAFE_INLINE
+from csp.constants import NONCE, NONE, SELF, UNSAFE_INLINE
 from decouple import Choices, Csv, config
 from sentry_sdk.integrations.django import DjangoIntegration
 from sentry_sdk.integrations.logging import ignore_logger
@@ -141,6 +141,7 @@ else:
 
 API_DOCS_ENABLED = config("API_DOCS_ENABLED", False, cast=bool) or DEBUG
 _CSP_SCRIPT_INLINE = API_DOCS_ENABLED or USE_SILK
+_CSP_SCRIPT_INLINE = False
 
 # When running locally, styles might get refreshed while the server is running, so their
 # hashes would get oudated. Hence, we just allow all of them.
@@ -189,21 +190,26 @@ CONTENT_SECURITY_POLICY: CONTENT_SECURITY_POLICY_T = {
         "default-src": [SELF],
         "connect-src": [
             SELF,
-            "https://www.google-analytics.com/",
-            "https://www.googletagmanager.com/",
+            "https://*.google-analytics.com",
+            "https://*.analytics.google.com",
+            "https://*.googletagmanager.com",
             "https://location.services.mozilla.com",
             "https://api.stripe.com",
             BASKET_ORIGIN,
         ],
         "font-src": [SELF, "https://relay.firefox.com/"],
         "frame-src": ["https://js.stripe.com", "https://hooks.stripe.com"],
-        "img-src": [SELF],
+        "img-src": [
+            SELF,
+            "https://*.google-analytics.com",
+            "https://*.googletagmanager.com",
+        ],
         "object-src": [NONE],
         "script-src": [
             SELF,
-            UNSAFE_INLINE,  # TODO: remove this temporary fix for GA4
+            NONCE,
             "https://www.google-analytics.com/",
-            "https://www.googletagmanager.com/",
+            "https://*.googletagmanager.com",
             "https://js.stripe.com/",
         ],
         "style-src": [SELF],
@@ -373,7 +379,7 @@ if DEBUG:
 
 MIDDLEWARE += [
     "django.middleware.security.SecurityMiddleware",
-    "csp.middleware.CSPMiddleware",
+    "privaterelay.middleware.EagerNonceCSPMiddleware",
     "privaterelay.middleware.RedirectRootIfLoggedIn",
     "privaterelay.middleware.RelayStaticFilesMiddleware",
     "django.contrib.sessions.middleware.SessionMiddleware",

pyproject.toml

@@ -51,6 +51,7 @@ module = [
     "botocore.exceptions",
     "codetiming",
     "csp.constants",
+    "csp.middleware",
     "debug_toolbar",
     "dj_database_url",
     "django_filters.*",