How do I make the script what takes whitelisted roblox accounts (or user id) from 3rd party website?

I'm making a Roblox whitelist system to a lua script and I want to make that the script take usernames (or user ids') from other website like this: https://opencup.ml/images/x7p1obct.png (screenshot) and makes the gui opened for this users.

If it's possible.

Hello i know what you're trying to find and here's the source: this is a youtube video tutorial

I'm really sorry that i can't paste the script in here i'm just in a hurry and ye, however i tried to help , cya.