express-extendcsp

Express middleware for altering the Content-Security-Policy on the fly. Mostly useful in development when you want to make sure that your debugging and stylesheet injection techniques work, but without compromsing the CSP you're running in production.

Examples I've seen so far:

• Webpack dev servers need connect-src ws://* to work in all scenarios
• Several CSS loaders need style-src blob: or style-src data: in development to be able to inject a stylesheet with proper source mapping in spite of https://bugs.chromium.org/p/chromium/issues/detail?id=649679#c19

Usage

Put express-extendcsp in your middleware stack before the middleware that sets your CSP, and pass it a config object with an add key, specifying which directives to add to the Content-Security-Policy header:

require('express')()
  .use(
    require('express-extendcsp')({
      add: {
        connectSrc: 'ws://*',
        styleSrc: ['blob:', 'data:'],
      },
    })
  )
  .use((req, res, next) => {
    res.setHeader(
      'Content-Security-Policy',
      "default-src 'self'; object-src 'none'"
    );
  });

Both camelCased and snake-cased directive names are supported, and you can supply the tokens to add as either a string or an array of strings.

Releases

Changelog