Unique device identification

Unique device identification

We are developing in-house web-based application for viewing data reports
while targeting on smartphones and tablets. Our customer asked us for
possibility that only certain devices could access the content. Hence we
use technologies based on javascript/HTML5 we are no capable of reading
unique ID like IMEI or device uuid. The idea is to be able to automaticly
create time-independent fingreprint of device with abovementioned
technologies.
The question is are we able to create unique device fingerprint with
javascript/HTML5?
The clue might be information available or known by browser (e.g.
http://browserspy.dk/)