Cors Helper

This piece of ExpressJs middleware exists to make it easier to configure CORS settings in a NodeJs app with either a list of blocked or allowed IPs/URLs/Domains.

Installation

npm install cors-helper

Usage

A somewhat standard Express app would setup some key pieces of middleware (body-parser, compression, helmet, etc), but rather than using cors middleware out-of-the-box (by default cors() will allow everything!), instead you can pass it a function to dynamically handle origins. This cors-helper package provides you two factory functions that will create that function for you (depending on whether you want to block or allow certain IPs/URLs/Domains).

const cors = require('cors')
const helmet = require('helmet')
const express = require('express')
const bodyParser = require('body-parser')
const compression = require('compression')
const { createBlockedListMiddleware } = require('cors-helper')

// An array of strings representing all the sites you DON'T want to allow
const listOfBadSites = require('./block_these_ips_and_domains.json')

const corsOptions = createBlockedListMiddleware(listOfBadSites)

const port = process.env.PORT || 5000

express()
  .use(bodyParser.json({ limit: '4mb' }))
  .use(bodyParser.urlencoded({ extended: true }))
  .use(compression)
  .use(cors(corsOptions))
  .use(helmet)
  .listen(port, () => console.log(`app is now listening on port ${port}`))

API

This package exports two named factory functions that take a list of IPs, URLs, and/or Domains that you will be able to allow or block when your cors middleware is set up.

• allowCrossDomainMiddleware - A common piece of middleware that is used (mostly) for local development to completely turn off cors validation by setting certain headers (not typically used in production)
• createBlockedListMiddleware - A function that takes an Array of (String) values that represent the IPs, URLs, and/or Domains to reject (everything else will be allowed)
• createAllowedListMiddleware - A function that takes an Array of (String) values that represent the IPs, URLs, and/or Domains to allow (everything else will be rejected)