Basically my goal is to have players type a temporary authentication code shown on a PHP webpage, in game, for them to access certain information on the webpage.

So it'll be something like:

1. Player open up xxxxxx.com/xxx.php
2. The webpage shows "Please enter your steam id"
3. After player enter steam id, the webpage shows "please type /xxx <Authentication Code>"
4. Player types "/xxx <Authentication Code>"
5. The plugin should detect based on the /xxx command, and sends a GET or POST request to a remote PHP webpage, like xxxx.com/auth.php?code=123123 for authentication.
6. If everything goes well, the xxx.php page shows certain information that I'd like to show. 

Sort of like linking discord accounts, but I'm doing temporary authentication here. 

If anyone knows there are any plugins that can do this, please do let me know. And if you are capable of developing such plugin, please also let me know. 

Well you can actually give every player auth code when he joins, and then just do that on your website or somewhere instead of getting code on website and then pasting it in game

Tbh I don't really have a preference of how it is done, as long as it's doable. But I don't have enough understanding to write my own C# codes. 

Hey,
Did your code should be one-time use or attached to a specific steamID?
Also, you'll probably need a Mysql database to store infos.