title: Write unique android device ID to firebase firestore on first login
body: <p>I've googled this for hours but can't seem to find an answer. </p>
  
  <p>I want to grab the unique device ID upon first login and store it in the users firestore document so that I can identify each device associated with that users account, I'm already using the onCreate firebase cloud function to generate fields upon first login but cannot figure out how to get the device to store its ID there. </p>
  
  <p>Any help would be much appreciated</p>