TLDR: I'm having trouble with setting up CSP for NextJS using Material-UI (server side rendering) and served by Nginx (using reverse proxy).

Currently I have issues with loading Material-UI stylesheet, and loading my own styles

using makeStyles from @material-ui/core/styles

NOTE:

• followed https://material-ui.com/styles/advanced/#next-js to enable SSR
  • https://github.com/mui-org/material-ui/tree/master/examples/nextjs
• I looked at https://material-ui.com/styles/advanced/#how-does-one-implement-csp but I'm not sure how I can get nginx to follow the nonce values, since nonce are generated as unpredictable string.

default.conf (nginx)

# https://www.acunetix.com/blog/web-security-zone/hardening-nginx/

upstream nextjs_upstream {
  server localhost:3000;

  # We could add additional servers here for load-balancing
}

server {
  listen $PORT default_server;

  # redirect http to https. use only in production
  # if ($http_x_forwarded_proto != 'https') {
  #   rewrite ^(.*) https://$host$request_uri redirect;
  # }

  server_name _;

  server_tokens off;

  proxy_http_version 1.1;
  proxy_set_header Upgrade $http_upgrade;
  proxy_set_header Connection 'upgrade';
  proxy_set_header Host $host;
  proxy_cache_bypass $http_upgrade;

  # hide how is app powered. In this case hide NextJS is running behind the scenes.
  proxy_hide_header X-Powered-By;

  # set client request body buffer size to 1k. Usually 8k
  client_body_buffer_size 1k;
  client_header_buffer_size 1k;
  client_max_body_size 1k;
  large_client_header_buffers 2 1k;

  # ONLY respond to requests from HTTPS
  add_header Strict-Transport-Security "max-age=31536000; includeSubdomains; preload";

  # to prevent click-jacking
  add_header X-Frame-Options "DENY";

  # don't load scripts or CSS if their MIME type as indicated by the server is incorrect
  add_header X-Content-Type-Options nosniff;

  add_header 'Referrer-Policy' 'no-referrer';

  # Content Security Policy (CSP) and X-XSS-Protection (XSS)
  add_header Content-Security-Policy "default-src 'none'; script-src 'self'; object-src 'none'; style-src 'self' https://fonts.googleapis.com/css?family=Roboto:300,400,500,700&display=swap ; form-action 'none'; frame-ancestors 'none'; base-uri 'none';" always;
  add_header X-XSS-Protection "1; mode=block";

  ssl_protocols TLSv1.2 TLSv1.3;
  ssl_prefer_server_ciphers on;

  location / {
    # limit request types to HTTP GET
    # ignore everything else
    limit_except GET { deny all; }

    proxy_pass http://nextjs_upstream;
  }
}

The solution I found was to add nonce value to the inline js and css in _document.tsx

_document.tsx

Generate a nonce using uuid v4 and convert it to base64 using crypto nodejs module. Then create Content Security Policy and add the generated nonce value. Create a function to accomplish to create a nonce and generate CSP and return the CSP string along with the nonce

Add the generated CSP in the HTML Head and add meta tags.

import React from 'react';
import Document, { Html, Head, Main, NextScript } from 'next/document';
import { ServerStyleSheets } from '@material-ui/core/styles';
import crypto from 'crypto';
import { v4 } from 'uuid';

// import theme from '@utils/theme';

/**
 * Generate Content Security Policy for the app.
 * Uses randomly generated nonce (base64)
 *
 * @returns [csp: string, nonce: string] - CSP string in first array element, nonce in the second array element.
 */
const generateCsp = (): [csp: string, nonce: string] => {
  const production = process.env.NODE_ENV === 'production';

  // generate random nonce converted to base64. Must be different on every HTTP page load
  const hash = crypto.createHash('sha256');
  hash.update(v4());
  const nonce = hash.digest('base64');

  let csp = ``;
  csp += `default-src 'none';`;
  csp += `base-uri 'self';`;
  csp += `style-src https://fonts.googleapis.com 'unsafe-inline';`; // NextJS requires 'unsafe-inline'
  csp += `script-src 'nonce-${nonce}' 'self' ${production ? '' : "'unsafe-eval'"};`; // NextJS requires 'self' and 'unsafe-eval' in dev (faster source maps)
  csp += `font-src https://fonts.gstatic.com;`;
  if (!production) csp += `connect-src 'self';`;

  return [csp, nonce];
};

export default class MyDocument extends Document {
  render(): JSX.Element {
    const [csp, nonce] = generateCsp();

    return (
      <Html lang='en'>
        <Head nonce={nonce}>
          {/* PWA primary color */}
          {/* <meta name='theme-color' content={theme.palette.primary.main} /> */}
          <meta property='csp-nonce' content={nonce} />
          <meta httpEquiv='Content-Security-Policy' content={csp} />
          <link
            rel='stylesheet'
            href='https://fonts.googleapis.com/css?family=Roboto:300,400,500,700&display=swap'
          />
        </Head>
        <body>
          <Main />
          <NextScript nonce={nonce} />
        </body>
      </Html>
    );
  }
}

// `getInitialProps` belongs to `_document` (instead of `_app`),
// it's compatible with server-side generation (SSG).
MyDocument.getInitialProps = async (ctx) => {
  const sheets = new ServerStyleSheets();
  const originalRenderPage = ctx.renderPage;

  ctx.renderPage = () =>
    originalRenderPage({
      enhanceApp: (App) => (props) => sheets.collect(<App {...props} />),
    });

  const initialProps = await Document.getInitialProps(ctx);

  return {
    ...initialProps,
    // Styles fragment is rendered after the app and page rendering finish.
    styles: [...React.Children.toArray(initialProps.styles), sheets.getStyleElement()],
  };
};

source: https://github.com/vercel/next.js/blob/master/examples/with-strict-csp/pages/_document.js

nginx config

make sure to remove adding header regarding Content Security Policy. It might override the CSP in _document.jsx file.

alternative solutions

Creating a custom server and injecting nonce and Content Security Policy that can be accessed in _document.tsx

• https://bitgate.cz/content-security-policy-inline-scripts-and-next-js/
• https://nextjs.org/docs/advanced-features/custom-server
• https://medium.com/weekly-webtips/next-js-on-the-server-side-notes-to-self-e2170dc331ff