CSP: add helper middleware (#12004)

Sometimes we need to add additional CSP headers
to views from third party apps, this middleware
helps with that, instead of subclassing and overriding URLs.

This will mainly be used on .com.

readthedocs/core/middleware.py

@@ -1,4 +1,5 @@
 import structlog
+from django.conf import settings
 from django.http import HttpResponse
 
 log = structlog.get_logger(__name__)
@@ -33,3 +34,46 @@ def __call__(self, request):
                     status=400,
                 )
         return self.get_response(request)
+
+
+class UpdateCSPMiddleware:
+    """
+    Middleware to update the CSP headers for specific views given its URL name.
+
+    This is useful for views that we don't have much control over,
+    like views from third-party packages. For views that we have control over,
+    we should update the CSP headers directly in the view.
+
+    Use the `RTD_CSP_UPDATE_HEADERS` setting to define the views that need to
+    update the CSP headers. The setting should be a dictionary where the key is
+    the URL name of the view and the value is a dictionary with the CSP headers,
+    for example:
+
+    .. code-block:: python
+
+       RTD_CSP_UPDATE_HEADERS = {
+           "login": {"form-action": ["https:"]},
+       }
+    """
+
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        response = self.get_response(request)
+
+        # Views that raised an exception don't have a resolver_match object.
+        resolver_match = request.resolver_match
+        if not resolver_match:
+            return response
+
+        url_name = resolver_match.url_name
+        update_csp_headers = settings.RTD_CSP_UPDATE_HEADERS
+        if settings.RTD_EXT_THEME_ENABLED and url_name in update_csp_headers:
+            if hasattr(response, "_csp_update"):
+                raise ValueError(
+                    "Can't update CSP headers at the view and middleware at the same time, use one or the other."
+                )
+            response._csp_update = update_csp_headers[url_name]
+
+        return response

readthedocs/settings/base.py

@@ -143,6 +143,7 @@ def SWITCH_PRODUCTION_DOMAIN(self):
     CSP_REPORT_URI = None
     CSP_REPORT_ONLY = False
     CSP_EXCLUDE_URL_PREFIXES = ("/admin/",)
+    RTD_CSP_UPDATE_HEADERS = {}
 
     # Read the Docs
     READ_THE_DOCS_EXTENSIONS = ext
@@ -349,6 +350,7 @@ def MIDDLEWARE(self):
             "allauth.account.middleware.AccountMiddleware",
             "dj_pagination.middleware.PaginationMiddleware",
             "csp.middleware.CSPMiddleware",
+            "readthedocs.core.middleware.UpdateCSPMiddleware",
             "simple_history.middleware.HistoryRequestMiddleware",
             "readthedocs.core.logs.ReadTheDocsRequestMiddleware",
             "django_structlog.middlewares.CeleryMiddleware",