generate own local ssl thanks to: https://stackoverflow.com/questions/21397809/create-a-trusted-self-signed-ssl-cert-for-localhost-for-use-with-express-node

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Mkcert from @FiloSottile makes this process infinitely simpler:

1. Install mkcert, there are instructions for macOS/Windows/Linux
2. mkcert -install to create a local CA
3. mkcert localhost 127.0.0.1 ::1 to create a trusted cert for localhost in the current directory
4. You're using node (which doesn't use the system root store), so you need to specify the CA explicitly in an environment variable, e.g: export NODE_EXTRA_CA_CERTS="$(mkcert -CAROOT)/rootCA.pem"
5. Finally run your express server using the setup described in various other answers (e.g. below)
6. boom. localhost's swimming in green.

Basic node setup:

const https = require('https');
const fs = require('fs');
const express = require('express');

const app = express();    
const server = https.createServer({
    key: fs.readFileSync('/XXX/localhost+2-key.pem'), // where's me key?
    cert: fs.readFileSync('/XXX/localhost+2.pem'), // where's me cert?
    requestCert: false,
    rejectUnauthorized: false,
}, app).listen(10443); // get creative