Auto navigation works by the means of sending Win-R <url> <enter> as a series of keystrokes. Given that the key is programmed with an URL in the form of
http://xxx, Windows will launch the current registered browser (which does not need to be IE) and navigate to that URL. Optionally, an OTP can be automatically appended to the URL, allowing direct authentication, i.e.
http://www.mysite.com/login?otp=clefcei ... bjeevvkdtg<enter>
Making it this way makes it a Windows specific feature. Maybe there is a Mac shortcut for doing the same, but then it would be a Mac specific feature.
Furthermore, this feature also requires configuration of the keyboard layout into the Yubikey. This means that if a key that is configured to work on a US keyboard is brought to France, it won't work.
It is a pretty cool function, but to me these issues are somewhat a turn-off...
The configuration flag ykFLAG_SEND_REF is used to prefix the OTP with the reference modhex string cbdefghijklnrtuv. This feature was added if there would be any problems with any keyboard layout that did not fit well with the modhex scheme. The server would then simply use the reference prefix string to make proper substitution of the characters in the OTP string. AFAIK, it seems like this feature is not needed.
Regards,
JakobE
Hardware- and firmware guy @ Yubico