Read cookies in Firebase GCP Functions using Hosting Rewrites

I’m using Firebase Functions, and Firebase Hosting. Hosting redirects all traffic to my function.

Request cookies are not available when requesting the Hosted site (i.e. not the cloud function URL). Is there no way to access request cookies?

I’m migrating a website to Firebase and was assuming I could follow basic web principals of having access to same-domain cookies.

const { runWith } = require('firebase-functions');
const cookieParser = require('cookie-parser');
const express = require('express');
const app = express();
app.use(cookieParser());

function handleRequest(req, res) {
  res.cookie('firebase1', 'test', {});

  if (process.env.HOSTNAME) {
    res.cookie('firebase2', 'test', {
      domain: process.env.HOSTNAME,
    });
  }
  res.cookie('firebase3', 'test', {
    domain: req.hostname,
  });
  return res.json({
    hostname: process.env.HOSTNAME,
    'req.cookies': req.cookies, // always empty
    'req.headers.cookie': req.headers.cookie, // always undefined
  });
}

app.get('*', handleRequest);
app.use(handleRequest);

exports.index = runWith({
  timeoutSeconds: 10,
  memory: '128MB',
}).https.onRequest(app);

firebase.json

{
  "functions": {
    "ignore": [
      "node_modules",
      ".git",
      "firebase-debug.log",
      "firebase-debug.*.log"
    ]
  },
  "hosting": {
    "public": "public",
    "ignore": ["firebase.json", "**/.*", "**/node_modules/**"],
    "rewrites": [
      {
        "source": "**",
        "function": "index"
      }
    ]
  }
}