Sunday, July 23, 2023

How to Validate CSRF Tokens in Next.js using NextAuth.js


In the world of web development, ensuring the security of user data is of utmost importance. As developers, it is our responsibility to implement measures that protect users from potential attacks. Cross-Site Request Forgery (CSRF) is one such threat that can compromise the integrity of a web application. In this blog post, we will dive into a code snippet that demonstrates how Next.js, in conjunction with the popular authentication library NextAuth.js, handles CSRF protection using NextAuth.js cookies to safeguard user information.

CSRF and Next.js with NextAuth.js

Next.js provides powerful features for building server-side-rendered and statically generated applications. Combining it with NextAuth.js, an authentication library for Next.js, allows developers to easily implement authentication and user sessions with built-in CSRF protection using NextAuth cookies.

Code Walkthrough

  1. The code starts by importing necessary modules, including createHash from the Node.js crypto library and NextApiRequest and NextApiResponse from the Next.js framework.
  2. The exported function takes two parameters: req (NextApiRequest) and res (NextApiResponse), representing the incoming request and the response to be sent back.
  3. The function begins by checking if the request contains a cookie header. Cookies are essential for CSRF protection, as they store the CSRF token required for validation.
  4. If no cookie header is found, the function returns a 403 status code and an error message indicating the absence of cookies.
  5. If cookies are present, the function extracts the raw cookie string from the request header and splits it into an array of individual cookies.
  6. The loop then iterates through the cookie array to find the CSRF token generated by the NextAuth.js library. The NextAuth.js cookies are named next-auth.csrf-token and _Host-next-auth.csrf-token. The _Host- the prefix is used on Vercel to prevent cookie collisions.
  7. Once the CSRF token and hash are obtained, the function proceeds to validate the token against the provided hash.
  8. The valid hash is computed by concatenating the request token with the NEXTAUTH_SECRET, sensitive value stored in the environment variables. The createHash function from the crypto library is used to generate a SHA-256 hash of the concatenated string.
  9. If the computed hash does not match the request hash, it indicates a potential CSRF attack, and the function returns a 403 status code and an error message.
  10. In case of any exceptions or errors during the process, the function catches them and returns a 500 status code with an appropriate error message.


Here we explored a code snippet that demonstrates how Next.js, in collaboration with the NextAuth. authentication library, handles CSRF protection using NextAuth.js cookies to safeguard user data and prevent unauthorized actions. By utilizing NextAuth.js cookies and computing secure hash values, developers can ensure that their Next.js applications remain secure and protected against CSRF attacks.

As developers, it is vital to understand the security mechanisms provided by frameworks and libraries and implement them effectively to build robust and trustworthy web applications. Combining the power of Next.js and NextAuth.js, we can create a seamless and secure user experience for our applications. Happy coding and stay secure!