簡單來說:

getDeviceToken 方法有三:

一、ionic Native Push (https://ionicframework.com/docs/v2/native/push/)

二、ionic Native Firebase (https://ionicframework.com/docs/v2/native/firebase/)

三、cordova FCM plugin (https://github.com/fechanique/cordova-plugin-fcm)

之前試用的方式是:
http://sueboy.blogspot.tw/2017/01/ionic2-fcm-send-message-to-device-token.html

.AngularFire2  authstate.auth.getToken()  is  JWT token for firebase