I'm developing a mobile web for android, iphone & blackberry. We should enforce license for users. Let us say this product comes with 3 types of license.
They say "if customer has purchased application for 3 users then he should be allowed to access the application only in 3 devices, when he tries to access the same in 4th device he should be sent to some error page"
Let me explain further, we are designing a table, order selection app for restaurant, where every table(or waiter) will have a mobile, he/she opens the application and orders for the selected table. In such case a web app can be accessed in any device and customer may buy and install the app on their server and ask every one to access. That means he'll buy the product for one device and uses in many. So through PHP we need to limit the product to only one device. Remember it can be any device he's wish whenever, whatever the device he might use application should be accessed by/on x devices.
How can we do this? Any suggestions are welcomed.
Thanks in advance.
(FWIW I'd be very skeptical of buying a product licenced per device rather than on the basis of a named user).
The problem will be differentiating between devices.
While browser finger printing can provide very impressive results these datasets are predominantly filled with desktop browsers - I suspect you would see a lot less variation between mobile browsers (when was the last time you installed a new font on your android / iphone).
make a database of allowed devices, and set those devices with a cookie or track the users ip address (not recommended since it changes). You might also want to look into UNIX timestamps for figuring out time operations related to this.