config

Displays a message on config pages indicating which config settings have been override by settings.  
There's a config setting where you can hide the actual values (so you can hide API key - you need to use config editor to edit that, there's no admin page)

Lock all configuration changes via the admin UI - e.g. if you need to lockdown a production environment.

config_readonly now has a whitelist, added via an array in settings.php.