Support http/https via listening to Apache access_log

[jp-bennett]

We already support sending a knock over http. The server detects this connection using pcap. With https, the url is encrypted in the ssl connection, and pcap can't sniff it.

As an alternative to pcap, and to add support for https, we should add the ability to watch an Apache access_log (and possibly other log types) for incoming requests that are actually spa strings.