How to know which player pressed a key?

So I am trying to do a script (located in ServerScriptService) that detects if a key is pressed so it will call a function, but I don't know how to get the name of the player who pressed it.

game:GetService("UserInputService").InputBegan:connect(function(inputObject, gameProcessedEvent)
    if inputObject.KeyCode == Enum.KeyCode.R then 
        print("fireball pls")
    end 
end)

I can't use LocalPlayer since it's a server-sided script.