Middleware problem in Vercel, Next Auth V5, "message": "There was a problem with the server configuration. Check the server logs for more information."

[rodrigc]

Environment

  System:
    OS: macOS 14.6.1
    CPU: (16) x64 Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
    Memory: 3.45 GB / 32.00 GB
    Shell: 5.9 - /usr/local/bin/zsh
  Binaries:
    Node: 22.7.0 - /usr/local/bin/node
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 9.9.0 - /usr/local/bin/pnpm
  Browsers:
    Chrome: 128.0.6613.119
    Edge: 128.0.2739.63
    Safari: 17.6
  npmPackages:
    next: latest => 14.2.3
    next-auth: beta => 5.0.0-beta.17
    react: ^18 => 18.3.0

Reproduction URL

https://github.com/rodrigc/next-auth-v5

Describe the issue

I'm having the same problem reported by @ephraim888sun in #10137 and #10136.

I also mentioned the problem in jherr/next-auth-v5#1 , but I think that this might be a next-auth bug, so reporting here also.

I am testing it out now, and I am having a problem when trying to run in Vercel.

1. I forked the repository: https://github.com/jherr/next-auth-v5 into https://github.com/rodrigc/next-auth-v5
2. I added an .env file with AUTH_SECRET
3. I added more debugging in the middleware: https://github.com/rodrigc/next-auth-v5/blob/main/src/middleware.ts#L9
4. Everything works fine when testing locally on my laptop.
5. When I deploy to Vercel, I see in my debugging that console.log(req.auth); shows:

Session: undefined
Auth object: {
  message: 'There was a problem with the server configuration. Check the server logs for more information.'
}

How to reproduce

1. Deploy to vercel

vercel deploy --target=preview

2. Access the URL of the application
3. Look at the Vercel logs

Expected behavior

req.auth and req.auth.user should be correctly populated

[rodrigc]

I did some more debugging, and discovered that in a Vercel deployment,
the AUTH_SECRET variable was not being picked up from the .env file in my repository, and was not being set. This was the source of the problem.

[rodrigc]

In NextAuthRequest, auth is defined as either a Session or null,

next-auth/packages/next-auth/src/lib/index.ts

Line 100 in 9e628b3

auth: Session | null

but in this case where AUTH_SECRET is not set, I am seeing auth being set to:

{
  message: 'There was a problem with the server configuration. Check the server logs for more information.'
}

Is the fact that auth is being set to { message: string } a bug? Or should the type of NextAuthRequest be changed to:

export interface NextAuthRequest extends NextRequest {
  auth: Session | null | { message: string }
}

[balazsorban44]

Reproduction is private/404s.

To answer your question, when deployed on Vercel, the preferred way to define variables is via the dashboard, not .env.

Can't tell more as there was no reproduction provided. Felel free to open a new issue with a public code repository