All cookies will be set to HttpOnly, SameSite=Lax and will be set to Secure if the application's AUTH0_BASE_URL is https.

The HttpOnly setting will make sure that client-side JavaScript is unable to access the cookie to reduce the attack surface of XSS attacks.

The SameSite=Lax setting will help mitigate CSRF attacks. Learn more about SameSite by reading the "Upcoming Browser Behavior Changes: What Developers Need to Know" blog post.

Many hosting providers will offer to cache your content at the edge in order to serve data to your users as fast as possible. For example Vercel will cache your content on the Vercel Edge Network for all static content and Serverless Functions if you provide the necessary caching headers on your response.

It's generally a bad idea to cache any response that requires authentication, even if the response's content appears safe to cache there may be other data in the response that isn't.

This SDK offers a rolling session by default, which means that any response that reads the session will have a Set-Cookie header to update the cookie's expiry. Vercel and potentially other hosting providers include the Set-Cookie header in the cached response, so even if you think the response's content can be cached publicly, the responses Set-Cookie header cannot.

Check your hosting provider's caching rules, but in general you should never cache responses that either require authentication or even touch the session to check authentication (eg when using withApiAuthRequired, withPageAuthRequired or even just getSession or getAccessToken).

The default server side error handler for the /api/auth/* routes prints the error message to screen, eg

try {
  await handler(req, res);
} catch (error) {
  res.status(error.status || 400).end(error.message);
}

Because the error can come from the OpenID Connect error query parameter we do some basic escaping which makes sure the default error handler is safe from XSS.

If you write your own error handler, you should not render the error message, or error and error_description properties without using a templating engine that will properly escape it for other HTML contexts first.

We also provide an Auth0 React SDK, auth0-react, which may be suitable for your Next.js application.

The SPA security model used by auth0-react is different from the Web Application security model used by this SDK. In short, this SDK protects pages and API routes with a cookie session (see "Cookies and Security"). A SPA library like auth0-react will store the user's ID Token and Access Token directly in the browser and use them to access external APIs directly.

You should be aware of the security implications of both models. However, auth0-react may be more suitable for your needs if you meet any of the following scenarios:

• You are using Static HTML Export with Next.js.
• You do not need to access user data during server-side rendering.
• You want to get the access token and call external API's directly from the frontend layer rather than using Next.js API Routes as a proxy to call external APIs