Identifying a device

I currently have an application that is open to the public and allows people to make payments.

The company is wanting to use an iPad as a kiosk with a terminal device to make the payments.
There will be dozens of iPads deployed and each iPad should only be able to be used with one particular terminal device. The terminal is hooked directly to a an ethernet on the network and the iPads with have cellular service, so the iPad and terminal will not physically be connected to each other.

I need to limit the ability to make the payments using the terminal device just to the iPads. Is there a way I can uniquely identify each of the iPad? Either through code or javascript? I would prefer to stay away from using a something in the query string to prevent possible browser snooping.