I've gotten to the stage where I can easily modify/create HTML pages for my OS to dish out upon request (entering either the hostname or ip into a web-browser). Now, I need to start looking into authentication so that only the intended admin is allowed in.
A few options have come to mind:
1: Only allow the webserver (DiNS) to acknowledge one computer (the server or any other machine on 'that end' of the network).
2: Use some sort of login screen to weed out the people that dont have the right credentials.
3: Use a third ethernet jack as the administration link (webserver only acknowledges request from the console port)... cisco style

I would really like to stick with a login screen, but are there any easily implemented public domain encryption schemes that would be suitable for the job?
Any other ideas/methods of accomplishing this?