Unable to connect to Firestore Emulator with preferRest: true

[lahirumaramba]

When REST fallback is enabled by setting preferRest: true, the fallback client obtains an authenticated google-auth-library client to communicate with the Firestore BE services.

If the emulator mode is enabled by setting FIRESTORE_EMULATOR_HOST env var, the rest client will look for application default credentials in the environment to initialize credentials to obtain an authenticated google-auth-library client. This step fails if there are no credentials set in the environment. Firestore Client should not use service account credentials to connect to the emulator even if the real service credentials are available, instead we should explicitly set emulator credentials on emulator mode.

We already set emulator credentials on gRPC mode by setting custom headers at:

nodejs-firestore/dev/src/index.ts

Line 1453 in 653a8e9

Authorization: 'Bearer owner',

but for some reason this is not effective on REST fallback.

Steps to reproduce:

• Setexport FIRESTORE_EMULATOR_HOST="localhost:8080"
• Remove any application default credentials from your environment:
  • unset GOOGLE_APPLICATION_CREDENTIALS
  • gcloud auth application-default revoke

import { Firestore } from '@google-cloud/firestore'

// Create a new client
const firestore = new Firestore({ preferRest: true })

async function quickstart() {
  // Obtain a document reference.
  const document = firestore.doc('posts/intro-to-firestore')

  // Enter new data into the document.
  await document.set({
    title: 'Welcome to Firestore',
    body: 'Hello World',
  })
  console.log('Entered new data into the document')
}
quickstart()

Expected:

• A new entry should be added to the Firestore Emulator

Actual:

• Error log:

(node:62230) UnhandledPromiseRejectionWarning: Error: Could not load the default credentials. Browse to 
https://cloud.google.com/docs/authentication/getting-started for more information.
    at GoogleAuth.getApplicationDefaultAsync (nodejs-firestore/node_modules/google-auth-
library/build/src/auth/googleauth.js:206:19)
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at async GoogleAuth.getClient (nodejs-firestore/node_modules/google-auth-library/build/src/auth/googleauth.js:638:17)
    at async GrpcClient.createStub (nodejs-firestore/node_modules/google-gax/build/src/fallback.js:211:35)
Caused by: Error
    at WriteBatch.commit (nodejs-firestore/node_modules/@google-cloud/firestore/build/src/write-batch.js:433:23)
    at DocumentReference.set (nodejs-firestore/node_modules/@google-cloud/firestore/build/src/reference.js:392:27)
    at quickstart (file://nodejs-firestore/node-js-firestore-repro.js:11:18)
    at file://nodejs-firestore/node-js-firestore-repro.js:17:1
    at ModuleJob.run (internal/modules/esm/module_job.js:152:23)
    at async Loader.import (internal/modules/esm/loader.js:166:24)
    at async Object.loadESM (internal/process/esm_loader.js:68:5)

Related to: firebase/firebase-admin-node#2016 🦕

[MarkDuckworth]

Requested a feature in google-gax to support the solution for this: googleapis/gax-nodejs#1409