Github auth working locally but not in Vercel. Using custom login page

[emertechie]

Github auth works fine locally but when I deploy my Next.js app to Vercel and click the login button on my custom login page, nothing happens. There's nothing in error or console logs and when I view network logs I just see a cancelled request POST'ing to my custom login page:

I've added the AUTH_SECRET, AUTH_GITHUB_ID, and AUTH_GITHUB_SECRET production environment variables.

Bizzarely, it did work one time - I was redirected to Github and then back to app. But when I logged out and tried again, I'm back to the situation above.

Here's my code in src/app/custom-login-page/page.tsx:

And signin imported from import { signIn } from "@/auth"; (see below)

Anyone got any ideas? I think I've followed all the guides, so really surprised this is proving so difficult.

UPDATE: I tried removing the pages entry from my authConfig (so it uses the built-in login page), and with that one change everything works perfectly - so the environment variables seem fine. Is using a custom login page just broken / flaky in the beta?

My auth config:

import type { NextAuthConfig } from "next-auth";
import GitHub from "next-auth/providers/github";
import Google from "next-auth/providers/google";

export const authConfig = {
  pages: {
    signIn: "/custom-login-page",
  },
  providers: [GitHub, Google],
  callbacks: {
    authorized: async ({ auth }) => {
      // Logged in users are authenticated, otherwise redirect to login page
      return !!auth;
    },
  },
} satisfies NextAuthConfig;

Auth.ts:

import NextAuth from "next-auth";
import { authConfig } from "./auth.config";

export const { handlers, signIn, signOut, auth } = NextAuth({
  ...authConfig,
});

Middleware:

import NextAuth from "next-auth";

import { authConfig } from "./auth.config";

export default NextAuth(authConfig).auth;

export const config = {
  matcher: [
    /*
     * Match all request paths except for the ones starting with:
     * - api (API routes)
     * - _next/static (static files)
     * - _next/image (image optimization files)
     * - favicon.ico, sitemap.xml, robots.txt (metadata files)
     */
    "/((?!api|_next/static|_next/image|favicon.ico|sitemap.xml|robots.txt).*)",
  ],
};

Versions:

    "next": "15.2.3",
    "next-auth": "^5.0.0-beta.25",
    "react": "^19.0.0",

[emertechie]

Coming back to it some days later, it all seems to be working now 🤷‍♂️ . Will close the issue