WP Shield

This plugin will allow you to secure your development, staging and UAT environments
with an http authentication block that can be controlled in admin but also turned
off via a declared variable in your config file. It allows you to bring your Database
back to non-production environments without having to physically turn off the plugin each time.

Variable: define('WP_SHIELD_UN', '');

This simple line of code (recommended to add to a file ignored by your code management
software and required into your wp_config.php file) will override the enabled flag
if the plugin’s settings. Enable in production and add the above code. If that
require file doesn’t exist in your other environments, it will prompt users for the
set username and password.