I don't know how in iOS. In Android you can take a look to https://developer.android.com/training/articles/user-data-ids and implement it in the "Android" platform specific code,
get mobile device unique id
Bhuwan
716
Reputation points
Is it possible to get Android or iOS device unique id and given access based on unique id if I approve particular device to access the page then it's accessable otherwise display message you are not authorize this page.