Hi,
Currently Adobe campaign doesn't allow(OOTB) you to register your mobile devices using your web application as a middle layer. I believe there is a way if you have the licence to use mobile app channel than you would have received two SDK from Adobe 1 for IOS APP(objective C) and another for Android.
In SDK, they are supporting Firebase Cloud Messaging (FCM). Using FCM, you can notify a client app that new email or other data is available to sync. You can send notification messages to drive user reengagement and retention. For use cases such as instant messaging, a message can transfer a payload of up to 4KB to a client app.
You can use the same feature to extend your functionality.
i.e.
NeolaneAsyncRunner neolaneObject = new NeolaneAsyncRunner(Neolane.getInstance());
neolaneObject.registerDevice(registrationToken, userKey, additionnalParam, this, new NeolaneAsyncRunner.RequestListener() ){..}
Regards,
Amit