Getting the user id from a Firestore Trigger in Cloud Functions for Firebase?

Question

In the example bellow, is there a way to get the user id (uid) of the user who wrote to 'offers/{offerId}'? I tried to do as described here but it doesn't work in Firestore.

exports.onNewOffer = functions.firestore
  .document('offers/{offerId}')
  .onCreate(event => {
    ...
});

Answer 1

I was struggling on this for a while and finally contacted the firebase Support:

The event.auth.uid is undefined in the event object for firestore database triggers. (It works for the realtime Database Triggers)

When I console.log(event) I can’t find any auth in the output.

The official support answer:

Sorry the auth is not yet added in the Firestore SDK. We have it listed in the next features.

Keep an eye out on our release notes for any further updates.

I hope this saves someone a few hours.

UPDATE:

The issue has been closed and the feature will never be implemeted:

Hi there again everyone - another update. It has been decided that unfortunately native support for context.auth for Firestore triggers will not be implemented due to technical constraints. However, there is a different solution in the works that hopefully will satisfy your use case, but I cannot share details. On this forum we generally keep open only issues that can be solved inside the functions SDK itself - I've kept this one open since it seemed important and I wanted to provide some updates on the internal bugs tracking this work. Now that a decision has been reached, I'm going to close this out. Thanks again for everyone's patience and I'm sorry I don't have better news. Please use the workaround referenced in here.