A virtual door.
 Knock Back Door (Server)
The server end is a listening TCP/IP Socket on port 8008 by default.
Server initiates a ServerSocket to listen on all available IPv4 IP's at port 8008 by default.
Server waits for any incoming socket requests. Accepts connection, triggers appropriate knock and status response to client.
 Knock Front Door (Client)
The client end is a socket request to the server at it's listening IP and port.
A knock request can be generated via http using a common GET request.
This can be used to test a local instance of the knock server by going to http://127.0.0.1:8008/knock