External Authentication

Hello, I need to make custom web management system. The application contains data about all our client (domain to connect to cpanel,username and password). I need to implement logic that gives us possibility to login directly into client panel and manage his/her hosting properties. There is a table with all clients and there is a button 'connect' that need to reconnect and login direct in client panel so we can manage all needed thing there. I have tried all solutions from dev documentation and they did not worked, so can anyone else help me and give me a solution or example of how i need to implement the logic for reconnection and login into panel. I have tried many ways like Basic Authentication etc. I am using PHP 7.*.