Can anyone make a plugin that lets you put in an html code that lets someone just put there name into a box and get auto whitelisted?
Be clear how. Your server must be running as a web server and be connected to the place you put the HTML. Maybe your server isn't online but then it must be connected somehow. I've no idea how you're gonna make that work without using some quite difficult web connector stuff. I definitely can't make this. It probably won't be just HTML, your server will have to support JavaScript, Java or PHP. Could be possible via <form> but that's kinda... old and unhandy. What I'm saying is, however it is, however the plugin works, it will be quite hard for you probably. And btw, I'm really very sure this plugin already exists. Probably several ones. But they're all private.
What would probably be easiest would be to either use something like JSONAPI or UrlManager. Then a separate web server could do the authentication and alert the server of new players who have been authenticated. It's really not terribly difficult. So... They exist, but no one can have them? ; )
Why so complicated? You can insert the names in a MySQL table and check inside the plugin if the name's table contains the name. If you want me to do that for you, I can do it. LG
Using an api allows the plugin to decide how information is stored AND allows it to change it without the websites that connect to it having to change. It's the whole concept of Interfaces in computer science 101. Making the website connect directly to the database is an "easy" design but makes more maintenance when the plugin changes and doesn't make use of code re-usability. The less number of entry points the better.