Next basePath not handled on signin page

[marcoreni]

Environment

System:
OS: macOS 14.2
CPU: (10) arm64 Apple M1 Pro
Memory: 149.20 MB / 32.00 GB
Shell: 5.9 - /bin/zsh
Binaries:
Node: 20.10.0 - ~/Library/Caches/fnm_multishells/2567_1703023890015/bin/node
Yarn: 1.22.19 - ~/.yarn/bin/yarn
npm: 10.2.3 - ~/Library/Caches/fnm_multishells/2567_1703023890015/bin/npm
pnpm: 8.12.1 - /opt/homebrew/bin/pnpm
bun: 0.5.8 - ~/.bun/bin/bun
Browsers:
Chrome: 120.0.6099.109
Safari: 17.2
npmPackages:
next: 14.0.4 => 14.0.4
next-auth: 5.0.0-beta.4 => 5.0.0-beta.4
react: 18.2.0 => 18.2.0

Reproduction URL

https://github.com/marcoreni/next-auth-repro-base-path

Describe the issue

My application has a basePath configured on "next" side. However, this is not fully handled properly on Next.

Session call work, redirection to signin page works, but the form action does not contain the

How to reproduce

1. Configure a basePath inside next.config.js
2. Configure the base path according to Next-Auth configuration (both NEXTAUTH_URL and basePath inside session provider)
3. Open the project and click on Signin. You will be redirected to /api/auth/signin instead of /{basePath}/api/auth/signin.

(NOTE: the repro repository has been configured with a base path of "/foo". If you open http://localhost:3000/foo/middleware-example , you will be redirected on the login page, and clicking on the Github button will yield the problem)

Expected behavior

The form action URL should include the basePath.

[jenewland1999]

Behaviour is still present in in Next.js v14.1 and next-auth v5 beta.5

[balazsorban44]

The next.config.js basePath cannot be propagated to NextAuth.js, so you need to manually add this as a prop to SessionProvider and to the NextAuthConfig.

[jenewland1999]

@balazsorban44 According to the types being shipped in beta.5, basePath is not a valid option for NextAuthConfig. Also, if we use App Router, do we still need SessionProvider to wrap the entire app in the Root Layout? The upgrade guide suggests it doesn't, but I thought I'd ask at least. Furthermore, does the AUTH_URL env var need the basePath on it too (i.e. http://localhost:3000/foo)

[balazsorban44]

Not shipped yet but it's here

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

Line 12 in b5d5f20

config.basePath ??= "/api/auth"

SessionProvider will likely be not needed in App Router at all. We'll document this soon.

[jenewland1999]

Okay, thank you. I'll keep an eye on the releases page for now. 😄

[hscstudio]

So, now, can I do for it? I must run Next 14 App router on sub directory, but fail becaus auth 5 not yet supported..

http://localhost:3000/admin

I have add in SessionProvider

and

in AuthConfig

basePath:"/admin/api/auth"

but still error

[neoplastic]

@hscstudio I'm getting this same problem. Mine says in the logs
Cannot parse action at /api/auth/callback/nodemailer. Read more at https://errors.authjs.dev#unknownaction

[mirkahromi]

The next.config.js basePath cannot be propagated to NextAuth.js, so you need to manually add this as a prop to SessionProvider and to the NextAuthConfig.

Could you please elaborate a bit more how to set them up?

[nktnet1]

Collection of workarounds I've found:

1. k3k8's solution
2. ThanhHuuVu's solution
3. andreynovikov's solution