Notification infrastructure for modern mobile apps

// Register multiple devices for a given user. Notifications
// will be delivered to each device in a single send call
{
  "tokens": [
    {
      "token": "abc123",
      "provider_key": "apn",
      "properties": {
        "test": true
      },
      "device": {
        "app_id": "com.my.app",
        "platform": "iOS",
        "model": "iPhone 13"
      }
    },
    {
      "token": "cba321",
      "provider_key": "firebase-fcm",
      "tracking": {
        "ip": "127.0.0.1",
        "lat": "0.0",
        "long": "123"
      }
    }
  ]
}