Improve security: HSTS, Force SSL, CSP

config/application.rb

@@ -16,6 +16,10 @@ module Projekteuler
     # -- all .rb files in that directory are automatically loaded after loading
     # the framework and any gems in your application.
 
+    config.action_dispatch.default_headers = {
+        'X-Frame-Options' => 'DENY'
+    }
+
     # Set Time.zone default to the specified zone and make Active Record auto-convert to this zone.
     # Run "rake -D time" for a list of tasks for finding time zone names. Default is UTC.
     # config.time_zone = 'Central Time (US & Canada)'