Specs for minimal CSP policy in Api:: controllers (#27845)

app/controllers/concerns/api/content_security_policy.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module Api::ContentSecurityPolicy
+  extend ActiveSupport::Concern
+
+  included do
+    content_security_policy do |policy|
+      # Set every directive that does not have a fallback
+      policy.default_src :none
+      policy.frame_ancestors :none
+      policy.form_action :none
+
+      # Disable every directive with a fallback to cut on response size
+      policy.base_uri false
+      policy.font_src false
+      policy.img_src false
+      policy.style_src false
+      policy.media_src false
+      policy.frame_src false
+      policy.manifest_src false
+      policy.connect_src false
+      policy.script_src false
+      policy.child_src false
+      policy.worker_src false
+    end
+  end
+end