How to set Access-Control-Allow-Headers header in node-http-proxy - node.js

Question

I am using the coinbase-pro library to make post request to the coinbase sandbox api through a form on localhost. I am trying to use node-http-proxy to get around a CORS error with no success. Ive been banging my head against the wall for a while on this, any help would be appreciated.
const express = require("express");
const httpProxy = require("http-proxy");
const port = 5050;
const app = express();
const proxy = httpProxy.createProxyServer({});
app.use(function(req, res) {
delete req.headers["origin"];
delete req.headers["referer"];
delete req.headers["host"];
res.setHeader("Access-Control-Allow-Origin", "*");
res.setHeader(
"Access-Control-Allow-Headers",
"Content-type, cb-access-key,cb-access-passphrase,cb-access-sign,cb-access-timestamp"
);
res.setHeader(
"Access-Control-Allow-Methods",
"GET,POST,PUT,DELETE,OPTIONS"
);
const apiURL = 'https://api-public.sandbox.pro.coinbase.com'
proxy.web(req, res, { target: apiURL });
});
app.listen(port, () =>
console.log("Started proxy on port", port)
);
error:
Access to fetch at 'http://localhost:5050/orders' from origin 'http://localhost:3000' has been blocked by CORS policy: Request header field cb-access-passphrase is not allowed by Access-Control-Allow-Headers in preflight response.

Answer 1

The answer is here:
I think modifying the proxy response header is not covered in the current doc.
proxy.on('proxyRes', function(proxyRes, req, res) {
console.log('Raw [target] response', JSON.stringify(proxyRes.headers, true, 2));
proxyRes.headers['x-reverse-proxy'] = "custom-proxy";
proxyRes.headers['cache-control'] = "max-age=10000";
console.log('Updated [proxied] response', JSON.stringify(proxyRes.headers, true, 2));
// Do not use res.setHeader as they won't override headers that are already defined in proxyRes
// res.setHeader('cache-control', 'max-age=10000');
// res.setHeader('x-reverse-proxy', 'custom-proxy');
});
The key is to use proxyRes inside "proxyRes" event like proxyRes.headers[key] = value instead of relying on res.setHeader(key, value) as res.setHeader does not work when key is already exists among the proxy target response headers.