I was wondering if it is possible to create a dedicated game server for a game that already exists and you don't have access to. For example, a game on Steam that only allows multiplayer through hosting a game with your running client. A client can host a server but only while the hoster is also playing the game.
The question being, is it possible to write a server from scratch that can replace the game client host with a dedicated server that does not require a player hosting it? If so, how?