next.config.js

// https://securityheaders.com
const ContentSecurityPolicy = `
  default-src 'self';
  script-src 'self' 'unsafe-eval' 'unsafe-inline' https://js.stripe.com;
  child-src https://*.stripe.com https://*.stripe.network;
  style-src 'self' 'unsafe-inline' https://*.stripe.com;
  img-src * blob: data: https://*.stripe.com;
  media-src 'none';
  connect-src *;
  font-src 'self';
  frame-src https://js.stripe.com https://*.auth0.com;
`;

const securityHeaders = [
  // https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP
  {
    key: 'Content-Security-Policy',
    value: ContentSecurityPolicy.replace(/\n/g, '')
  },
  // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Referrer-Policy
  {
    key: 'Referrer-Policy',
    value: 'origin-when-cross-origin'
  },
  // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options
  {
    key: 'X-Frame-Options',
    value: 'DENY'
  },
  // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Content-Type-Options
  {
    key: 'X-Content-Type-Options',
    value: 'nosniff'
  },
  // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-DNS-Prefetch-Control
  {
    key: 'X-DNS-Prefetch-Control',
    value: 'on'
  },
  // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Strict-Transport-Security
  {
    key: 'Strict-Transport-Security',
    value: 'max-age=31536000; includeSubDomains; preload'
  },
  // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Feature-Policy
  // Opt-out of Google FLoC: https://amifloced.org/
  {
    key: 'Permissions-Policy',
    value: 'camera=(), microphone=(), geolocation=()'
  }
];

module.exports = {
  poweredByHeader: false,
  images: {
    domains: ['files.stripe.com']
  },
  async headers() {
    return [
      {
        // Apply these headers to all routes in your application.
        source: '/(.*)',
        headers: securityHeaders
      }
    ];
  }
};