A Wolff project can enter into maintenance mode quite easily.
The constant maintenance_on defined in the config.php file indicates if the project is under maintenance or not, just change its value to true if you want to activate it.
When under maintenance, a default _maintenance.php controller will be called if the client IP address isn't in the white list.
A white list file is the one that defines which IP address will still have access to the page content when it's under maintenance.
It should be located under the system/definitions directory and should be named maintenance_whitelist.txt.
You can create it in a fast way calling the createFile method:
Maintenance::createFile();
Adding an IP address to the white list:
Maintenance::addAllowedIP('127.0.0.1');
If the white list file doesn't exists, it will be created automatically.
Deleting an IP address from the white list:
Maintenance::removeAllowedIP('127.0.0.1');
Get all the IP address in the white list:
Maintenance::getAllowedIPs();
This will return the IP list as an array.
You can know if the current client IP address is in the white list with the following method:
Maintenance::isClientAllowed();
Remember that you can add and remove IPs using the CLI of Wolff too.