Push notificatin to custom user id


I am trying to implement push notification into my basic application.
following the guide i could receive the simplest push notification in my browser using tokenid
however in my project i would like to register for push notification after user logs in.
But the problem is, i have to send push notification based on custom user id, which i get after logging in.
could u give me some resources where i can read some possible solutions to this ?
Maybe after log in i should send registration token and custom user id to my backend and store in db ?


im having the same problem. it explains how to do general push notifications but not how to do especific notifications from my backend. did you solve the problem?