Why Isn't the Token Being Saved in the Cookie?

In web development, we occasionally come across issues that are puzzling and time-consuming to solve. One such issue that I recently faced involved JWT tokens not being stored in cookies for specific users. I invested several days trying to resolve this issue and eventually found a solution. In this blog post, I will share the details of the problem and the steps I took to resolve it.

Problem:

In my web application, I utilized JWT (JSON Web Token) for user authentication. After a successful login, the server would send a JWT token to the client, which was supposed to be stored in a cookie. However, for certain users, the token was not being stored in the cookie. The perplexing part was that this issue only occurred for specific users and was not consistent across all users.

Investigation:

I began by examining the server's response headers for the problematic users. To my astonishment, the "Set-Cookie" header was present, and a token was indeed being sent. Nonetheless, the token was not appearing in the browser's cookie storage. After a deeper investigation, I noticed that the problematic users had an unusually long token compared to other users.

The following code was creating tokens that were too long, causing the problem:

Root Cause:

It became clear that the issue stemmed from the token's size. For the problematic users, the JWT token was too large to be stored in a cookie. Browsers impose a limit on the maximum size of a cookie, and the token was exceeding this limit. This occurred because the token payload for these users contained a large amount of data, making the token exceptionally lengthy.

const payload = {
  firstName: userInfo.firstName,
  lastName: userInfo.lastName,
  email,
  id: userInfo._id,
  followers: userInfo.followers,
  userIcon: userInfo.userIcon,
  following: userInfo.following,
  bio: userInfo.bio,
};

const token = await signToken(payload, secret);

Solution:

To address the problem, I modified the token generation logic to include only essential information in the payload. By reducing the amount of data in the token, I was able to ensure that the token's size remained within the limits imposed by browsers. After implementing this change, the tokens were successfully stored in the cookies for all users.

I revised it to the following:

const payload = {
  id: userInfo._id,
  email,
};

const token = await signToken(payload, secret);

This issue underscored the importance of considering the size of data being sent in tokens and cookies. By including only essential information in the token and ensuring that its size stays within the browser's limits, I was able to avert this problem in the future. I hope that sharing my experience will be helpful to others facing similar challenges.