Using Google Authenticator, https://code.google.com/p/google-authenticator/, their 30 second TOTP to protect a page or post. Initial release gives you a menu in the Tools section of the admin area to setup new keys for use. Gives you a link that can be used as a QR Code img src link or you can browse to it and see the graphic there as well. By setting up the QR Code/Link in your Google Authenticator App you are then able to use that 30 second temporary password to protect a page or post. It uses session variables to make it so once you are logged in to that page you can browse away from it and still go back to the page after 30 seconds.
A Meta Box within the pages and posts area allow you to enable protection as well as the ability to check any number of keys that can access the page.
Scan the below QR Code into your Google Authenticator App on your phone and you will be able to see the Protected Test Page.
Protected Test Page: https://www.gregwhitehead.us/protected-page/
URL for Google Authenticator App that also is the below QR Code: https://chart.googleapis.com/chart?chs=200×200&chld=M|0&cht=qr&chl=otpauth%3A%2F%2Ftotp%2FGregs+QR+For+Test+Page%3Fsecret%3DL7VH3R6LQX2JXJEI