NextAuth.js signIn() method not working using serverless-http in AWS Lambda - next.js

Question

I am trying to deploy NextJs and NextAuth.js to AWS using CDK (Cloud Development Kit). I have cloned the NextAuth.js example project (https://github.com/nextauthjs/next-auth-example) and
installed "serverless-http" for handling the binding from Lambda to NextJs. I attempted to follow this guide https://remaster.com/blog/nextjs-lambda-serverless-framework but using AWS CDK instead of the serverless.yml file as I am integrating it with existing infrastructure.
next.config.js:
/** #type {import('next').NextConfig} */
const nextConfig = {
reactStrictMode: true,
swcMinify: true,
images: {
unoptimized: true
},
output: 'standalone'
}
module.exports = nextConfig
[...nextauth].ts (From the example but using a simple credentials provider that always resolves):
import NextAuth, { NextAuthOptions } from "next-auth"
import CredentialsProvider from "next-auth/providers/credentials";
export const authOptions: NextAuthOptions = {
providers: [
CredentialsProvider({
name: "Credentials",
credentials: {
username: { label: "Username", type: "text", placeholder: "jsmith" },
password: { label: "Password", type: "password" }
},
async authorize(credentials, req) {
return { id: "1", name: "J Smith", email: "jsmith#example.com" }
}
})
],
theme: {
colorScheme: "light",
},
callbacks: {
async jwt({ token }) {
token.userRole = "admin"
return token
},
},
}
export default NextAuth(authOptions)
server.ts:
import { NextConfig } from "next";
import NextServer from "next/dist/server/next-server";
import serverless from "serverless-http";
// #ts-ignore
import { config } from "./.next/required-server-files.json";
const nextServer = new NextServer({
hostname: "localhost",
port: 3000,
dir: __dirname,
dev: false,
conf: {
...(config as NextConfig),
},
});
export const handler = serverless(nextServer.getRequestHandler());
It is being built using the following script:
#!/bin/bash
BUILD_FOLDER=.dist
yarn build
rm -rf $BUILD_FOLDER
mv .next/standalone/ $BUILD_FOLDER/
cp -r .next/static $BUILD_FOLDER/.next
rm $BUILD_FOLDER/server.js
cp -r next.config.js $BUILD_FOLDER/
cp -r node_modules/serverless-http $BUILD_FOLDER/node_modules/serverless-http
tsc server.ts --outDir .dist --esModuleInterop true
cp -r public $BUILD_FOLDER/
This is deployed using AWS written in CDK C#. Primarily using a HttpApi and a single Lambda. Each configured as shown below:
Lambda:
var function = new Function(this, "nextjs-function", new FunctionProps
{
Code = Code.FromAsset(...".dist"),
Handler = "server.handler",
Runtime = Runtime.NODEJS_16_X,
...
Environment = new Dictionary<string, string>
{
{ "NEXTAUTH_URL", "https://myDomainName.com" },
{ "NEXTAUTH_SECRET", portalSecret },
}
});
HttpApi:
var httpApi = new HttpApi(this, "http-api", new HttpApiProps
{
DisableExecuteApiEndpoint = true,
DefaultIntegration = new HttpLambdaIntegration("nextjs-route", function),
DefaultDomainMapping = new DomainMappingOptions
{
DomainName = "myDomainName.com"
}
});
Opening the deployed webpage and clicking the "Sign In" button at the top, I get taken to /api/auth/signin?callbackUrl=%2F with a form. Without touching the credentials I click "Sign in with credentials". This results in the page reloading and nothing happening. Expected behaviour should be a session and a redirect back to the home page (/) as is happening when running it locally using either yarn dev or yarn build && yarn start.
I get no errors client/server-side thus leaving me in the dark.
I suspect that it has to do with domain configuration but I am unable to find the problem. I tested with another NextJs/NextAuth project using a AWS Cognito provider. This also had problems as when I clicked the sign in button I got an "Unexpected token" error due to the underlying signIn(...) function (from the NextAuth library) trying to parse the fetched page as JSON, which turned out to be the sign-in-page. Thus my suspicion of something domain-related.