Custom Express server seemingly makes Next-Auth call wrong URL?

[Knockturnal]

Hello, Next-Auth community!

I'm having an issue with Next-Auth. I've set the NEXTAUTH_URL to the correct (deployment) URL, which is running on port 443. (I've replaced the url with https://example.com/ in the snippets below.)

This was working fine, however after I implemented a custom Express server in place of the default Next I get this error:

[next-auth][error][CLIENT_FETCH_ERROR]
https://next-auth.js.org/errors#client_fetch_error request to http://localhost:3000/api/auth/session failed, reason: connect ECONNREFUSED 127.0.0.1:3000 {
  error: {
    message: 'request to http://localhost:3000/api/auth/session failed, reason: connect ECONNREFUSED 127.0.0.1:3000',
...

All pages/routes work as expected from the browser. (But are obviously broken by the fact that the client can't get a session)

I can call my APIs manually like https://example.com/api/auth/session and that works, but for some reason Next-Auth is trying to connect at the wrong port (3000? And the wrong protocol it seems). I even log the NEXTAUTH_URL when starting my server and it does indeed show the correct URL https://example.com/

Since this started happening when I replaced the server with a custom Express server I assume that must be the catalyst, but the routing seems to work fine otherwise. Any ideas?

My custom server looks like this (partial):

const https = require("https"); //TLS
const express = require("express"); //Express webserver
const next = require("next");
const { parse } = require("url");

const nextApp = next({ dev: true, hostname: "localhost", port: port });
const handle = nextApp.getRequestHandler();
const expressApp = express();
const port = 443;

async function StartExpress() {
    await nextApp.prepare();

    //  Custom routes go here... eventually

    //    Hand all other routes to Next
    expressApp.all("*", (req, res) => {
        const parsedUrl = parse(req.url, true);
        return handle(req, res, parsedUrl);
    });

    console.log(process.env.NEXTAUTH_URL); //  https://example.com - seems to work as intended

    const server = https.createServer(httpsOptions, expressApp);
    server.listen(port, (err) => {
        if (err) throw err;
        console.log("Running on port " + server.address().port);
    });
}

StartExpress();

Also, it seems something is calling the appropriate endpoint, if I monitor the server I do get a call to https://example.com/api/auth/session - so for some reason it IS calling it, but it's not working and still complaining that it can't call http://localhost:3000

I assume my blunder lies somewhere in wrapping the next routing in express, however I just can't figure it out. Any help would be greatly appreciated.

[Knockturnal]

As per usual I figured this out just after formulating this question. It turned out I was importing next-auth in the server, which is not supported and was accidental. Probably caused by overly eager auto-complete.

const { getSession } = require("next-auth/react")