Creating a server admin api to manage a server from outside of the Unity app?

I've never written an API before and I'm curious how something like this might be done for a Unity game. Server runs as a Unity app -- I want server admins to be able to manage their servers remotely? What are some of my options? There any resources you can point me to? I'm not necessarily looking for code snippets -- a more general description of the setup would be greatly appreciated.

How would the server receive commands? Direct socket connection with another app? What if I wanted the server admin interface to be web-based?

Thanks.

 

If you want a web based interface why not run a C# webserver from your Unity instance?

There are loads of examples on codeproject and the like and you could easily serve dynamic content from it