Unexpected token < in JSON at position 0

[saito-kosuke]

Environment

System:
OS: macOS 11.6.6
CPU: (16) x64 Intel(R) Xeon(R) W-2140B CPU @ 3.20GHz
Memory: 368.77 MB / 32.00 GB
Shell: 3.2.57 - /bin/bash
Binaries:
Node: 18.12.0 - ~/.nodebrew/current/bin/node
Yarn: 1.22.0 - ~/transcope/node_modules/.bin/yarn
npm: 8.19.2 - ~/.nodebrew/current/bin/npm
Watchman: 4.9.0 - /usr/local/bin/watchman
Browsers:
Chrome: 109.0.5414.87
Firefox: 105.0.2
Safari: 14.1.2
npmPackages:
next: 13.1.1 => 13.1.1
next-auth: 4 => 4.18.8
react: 18.2.0 => 18.2.0

Reproduction URL

http://localhost:3000/api/auth/session

Describe the issue

[next-auth][error][CLIENT_FETCH_ERROR]
https://next-auth.js.org/errors#client_fetch_error Unexpected token < in JSON at position 0 {
error: {
message: 'Unexpected token < in JSON at position 0',
stack: 'SyntaxError: Unexpected token < in JSON at position 0\n' +
' at JSON.parse ()\n' +
' at Response.json (node:internal/deps/undici/undici:6160:23)\n' +
' at process.processTicksAndRejections (node:internal/process/task_queues:95:5)',
name: 'SyntaxError'
},
url: 'http://localhost:3000/api/auth/session',
message: 'Unexpected token < in JSON at position 0'
}

How to reproduce

access http://localhost:3000/api/auth/session

Expected behavior

The error won't occur

[github-actions[bot]]

We cannot recreate the issue with the provided information. Please add a reproduction in order for us to be able to investigate.

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Please test your reproduction against the latest version of NextAuth.js (next-auth@latest) to make sure your issue has not already been fixed.

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Useful Resources

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[kriscarle]

If you use Sentry, I got this same error today caused by newer versions of@next/sentry breaking next.config.js so my basePath setting wasn't loading getsentry/sentry-javascript#6447

Though according to the docs the most common cause for this error is not having NEXTAUTH_URL set correctly see https://next-auth.js.org/errors#client

[saito-kosuke]

@kriscarle
Thank you for your information.
I don't use Sentry, and I set NEXTAUTH_URL up as below. Is that right?
NEXTAUTH_URL="http://localhost:3000/api/auth"

[sync-adm]

@saito-kosuke I'm facing the same problem here, it's been a few hours. Did you manage to find any solution for this?

[jsjoeio]

Same as well. Any updates?

[floriaaan]

Still getting the same issue

[kriscarle]

For everyone ending up here with the client fetch error. It is a very generic error that normally means you do not have next-auth setup correctly, I'd recommend:

1. check that you have the API setup in /pages/api see https://next-auth.js.org/getting-started/example
2. check that you have set the NEXTAUTH_URL environment variable. In development that would normally be http://localhost:3000/api/auth in production it needs to be your actual domain. More help on setting variables in Nextjs https://nextjs.org/docs/pages/building-your-application/configuring/environment-variables
3. Try going to the API in your browser, the default would normally be http://localhost:3000/api/auth/session It returns the session object as JSON or an empty object if you are not authenticated. If you get a 404 or 500 error page instead, something isn't right.
4. If you are running a production build, make sure you are not loading your dev config, localhost:3000 won't work

If none of that works you'll need to share more details of your setup before anyone here could really help.

@saito-kosuke At first I thought the production config might be your problem because of the Xeon processor, but then I saw the macOS 11.6 part :)

[floriaaan]

I was getting this issue when updating next-auth from 4.15 to latest (4.20), I think I have properly setup my project (https://github.com/floriaaan/meet-at-cesi) and when I go to /api/auth/session, it returns my session..

[martinpachecolink]

In my case, I had this matcher value in the config var of the middleware file: "/api/:path*". it seems like the middleware does not allow to get to the other next-auth default endpoints.

[arthurpbarros]

This was actually my problem, when putting the path /api/:path* in the middleware matcher variable, the middleware prevents NextAuth from accessing the /api/auth/session route to authenticate.

My middleware looked like this after removing /api/:path*, it works perfectly:

export const config = {
  //remove '/api/:path*'
  matcher: ['/dashboard/:path*','/login','/api/posts','/api/users','/api/login']
}