In case anyone ever comes back to this and cares enough about the secret ending, I found it organically. It goes as follows:
- During the hack into AEGIS to find the password to your encrypted file, you'll be able to access John's personal laptop (the guy who runs AEGIS). Hack into and memdump this laptop.
- If you look at the image on the produced memdump, you'll get a picture of an eye and in the files, the line "ASCII85"*. The latter is a clue for decoding the former, producing the phrase "Do you like secrets?" which is also found in the description above next to a string of encoded text. That translates to "To see the secrets within the eye, you must find clarity on the center of the third eye. Only light will grant you the secret path of this extension."
- Given the eye in the image file, these must relate. In fact, if you either turn your screen brightness up a lot (or get a good angle) then you can see an IP address in the middle of the eye's pupil. Connect to the IP.
- You can't see anything or hack it without an SSL trojan which is never used in the extension, but at some point [not sure when exactly but presumably late game], one is quietly uploaded into your drop server, same place as you get webserverworm and the like.
- After breaking in you'll find out what to do next pretty clearly.

*this might be from another dump in the same progress, I can't quite recall