Webknock is a program that continuously scans Apache’s access logfile and executes a configurable command when a certain URL sequence is detected. The IP address of the client can be passed to the command to be executed, allowing one to use iptables to open certain ports (usually, SSH) to certain hosts as soon as the correct URL sequence is activated. No changes to the Web server configuration are necessary.
You can download it from the following link: https://packetstormsecurity.com/files/download/42719/webknock.tgz
Source: https://packetstormsecurity.com/files/42719/webknock.tgz.html