Evidence for a possible Windows Phone version of Valve's Steam Authenticator has been found inside the code for the Steam PC game download service.
References to Windows Phone and "WinRT" have been found in the code from a recent Steam update. That code was posted on Github (via Softpedia). Valve has released authenticator features in its Steam mobile app for iOS and Android. It allows Steam gamers to get a random code that can be used to log into their account for better security.
Valve has never indicated that it has any plans to support Windows Phone or Windows 10 on PC and Mobile in terms of such an app, and it's more than possible that the code references are just placeholders. Bearing all that in mind, would you want to have an official Steam authenticator app for the Windows platform? Let us know your thoughts in the comments!