Unexpected CORS Errors When Using Express with a Proxy Server
I'm deploying to production and I can't seem to get I'm working with unexpected CORS issues when trying to access my Express API from a front-end application running on a different origin. My front-end is served from `http://localhost:3000`, while my Express server is running on `http://localhost:5000`. I have set up CORS in my Express app using the `cors` middleware, but I'm still getting the following behavior in the browser console: ``` Access to XMLHttpRequest at 'http://localhost:5000/api/data' from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. ``` Here’s how I configured CORS in my Express app: ```javascript const express = require('express'); const cors = require('cors'); const app = express(); app.use(cors()); // I thought this would allow all origins app.get('/api/data', (req, res) => { res.json({ message: 'Hello, World!' }); }); app.listen(5000, () => { console.log('Server running on http://localhost:5000'); }); ``` I've confirmed that my server is correctly running and accessible via Postman at `http://localhost:5000/api/data`. I even tried specifying the origin explicitly in the `cors` options: ```javascript app.use(cors({ origin: 'http://localhost:3000' })); ``` Despite this, I'm still working with the same CORS scenario. Additionally, I have a reverse proxy set up using Nginx, but I'm not sure if it's interfering with the CORS headers. The Nginx configuration looks like this: ```nginx server { listen 80; server_name myapp.local; location / { proxy_pass http://localhost:5000; proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme; } } ``` I’ve tried various combinations of settings and even restarted both my Express server and Nginx, but nothing seems to resolve this question. Any insights on what might be going wrong or how to properly configure CORS in this scenario would be greatly appreciated! I recently upgraded to Javascript 3.11. This is happening in both development and production on Windows 10. Could this be a known issue?