NextAuth doesn't show basePath

[thebetterjort]

My setup works perfectly locally in docker, but when I try and deploy to a server behind a nginx proxy I'm not able to set the correct url for nextauth and it shows 404 error for

/api/auth/session
/api/auth/_log

I've set this up in my .env.local:
NEXTAUTH_URL=https://example.com/fpd/api/auth

next.config.js
module.exports = {
basePath: '/fpd',