Issue configuring proxy.ts with NextAuth v5 (authConfig split for Edge compatibility)

[martinestiga]

Hi!

I'm migrating to Next.js 16 and trying to configure the new proxy.ts with NextAuth 5.0.0-beta.30. I have split my auth configuration into two files (as recommended for non-Edge compatibility), following the documentation:
https://authjs.dev/getting-started/migrating-to-v5#edge-compatibility

My proxy.ts currently looks like this:

import authConfig from '@/lib/auth.config';
import NextAuth from 'next-auth';

export const { auth: proxy } = NextAuth(authConfig);

But Next.js throws this error when building:

 ⨯ The file "./proxy.ts" must export a function, either as a default export or as a named "proxy" export.
This function is what Next.js runs for every request handled by this proxy (previously called middleware).

Could someone please clarify how to correctly define the proxy.ts for Next.js 16 with NextAuth v5 when auth configuration is split into two files (non-Edge)?

Thanks in advance!