Hello, Blockstack using Docker -- CORS Error

I’ve build ‘Hello blockstack’ using a docker image based on node:alpine using express and cors but I continue to get the following CORS failure when I try to signin:

Access to fetch at ‘http://localhost:3000/manifest.json’ from origin ‘https://browser.blockstack.org’ has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource. If an opaque response serves your needs, set the request’s mode to ‘no-cors’ to fetch the resource with CORS disabled.

My server is pretty simple:
const express = require(‘express’);
const cors = require(‘cors’);
const app = express();
const port = 3000;

app.use(express.static(__dirname + ‘/’));

app.get(’/’, function(req, res) {

Any idea what would be causing this?