ExpressAuth ignores AUTH_URL and basePath

[noam-honig]

Environment

  System:
    OS: Windows 11 10.0.22631
    CPU: (16) x64 Intel(R) Core(TM) i7-7820X CPU @ 3.60GHz
    Memory: 7.70 GB / 31.68 GB
  Binaries:
    Node: 20.14.0 - C:\Program Files\nodejs\node.EXE
    npm: 10.7.0 - C:\Program Files\nodejs\npm.CMD
    pnpm: 8.15.6 - ~\AppData\Roaming\npm\pnpm.CMD
  Browsers:
    Edge: Chromium (127.0.2651.74)
    Internet Explorer: 11.0.22621.3527
  npmPackages:
    @auth/express: ^0.6.1 => 0.6.1
    react: ^18.3.1 => 18.3.1

Reproduction URL

https://github.com/noam-honig/demo-auth-problem-with-proxy

Describe the issue

I'm developing an app, using vite frontend with express and ExpressAuth as the backend.

I'm using vite's proxy option (in the vite.config.ts file to forward api and auth requests to the express backend on port 3002.

When I navigate to:
localhost:5173/auth/signout
And click ok - it navigates to:
localhost:3002 <-- the port for the backend
Instead of to localhost:5173 that I wanted.

I tried setting the AUTH_URL in the .env file - but:
a. It was ignored
b. it gave the following warning in the code: [auth][warn][env-url-basepath-redundant] Read more: https://warnings.authjs.dev#env-url-basepath-redundant

How to reproduce

1. Clone the repo
2. npm i
3. Open two terminals
   3.1. run npm run dev in the first
   3.2 run 'npm run dev-node' in the second
4. navigate to the url http://localhost:5173/auth/signout
5. Click sign out

it'll take you to localhost:3002 and not 5173

Try setting the AUTH_URL in the .env
it'll give the following warning in the console:
[auth][warn][env-url-basepath-redundant] Read more: https://warnings.authjs.dev#env-url-basepath-redundant
even when basePath wasn't set

Expected behavior

1. Best result - will go back to the localhost:5173 without any configuration.
2. I can live with setting the AUTH_URL in the .env file - but that it'll be used

[hillac]

I think what you want to set is the callbackUrl option, not the AUTH_URL env var. You'll have to allow it to redirect the the front end in the redirect callback in your config, or set callbackUrl to a route in the backend whose handler redirects you to the front end.

[noam-honig]

@hillac I'll look into that - but please don't skip the second part, where if I set AUTH_URL in the .env - it gives the error and is ignored.

[hillac]

Yeah, the maintainers added this line here:

next-auth/packages/frameworks-express/src/index.ts

Line 164 in 538dd77

config.basePath = getBasePath(req)

It auto sets the basePath from the route so you shouldn't need to set it. The setEnvDefaults function will ignore the AUTH_URL if baseUrl is already set.