Use example from authjs.dev (#118)

auth.ts

@@ -6,7 +6,7 @@ import { MongoDBAdapter } from '@auth/mongodb-adapter'
 import type { NextAuthConfig } from 'next-auth'
 import { findOneTyped } from './lib/db/dbTyped'
 import { Types } from './types/Components'
-import clientPromise from './lib/db/mongoDB'
+import client from './lib/db/authDbClient'
 
 export const authOptions: NextAuthConfig = {
   providers: [Discord],
@@ -85,7 +85,7 @@ export const authOptions: NextAuthConfig = {
   },
 
   // A database is optional, but required to persist accounts in a database
-  adapter: MongoDBAdapter(clientPromise, {
+  adapter: MongoDBAdapter(client, {
     collections: {
       Users: 'nextauth_users',
       Sessions: 'nextauth_sessions',

lib/db/authDbClient.ts

@@ -0,0 +1,37 @@
+// This approach is taken from https://github.com/vercel/next.js/tree/canary/examples/with-mongodb
+import { MongoClient, ServerApiVersion } from 'mongodb'
+
+if (!process.env.DATABASE_URL) {
+  throw new Error('Invalid/Missing environment variable: "DATABASE_URL"')
+}
+
+const uri = process.env.DATABASE_URL
+const options = {
+  serverApi: {
+    version: ServerApiVersion.v1,
+    strict: true,
+    deprecationErrors: true,
+  },
+}
+
+let client: MongoClient
+
+if (process.env.NODE_ENV === 'development') {
+  // In development mode, use a global variable so that the value
+  // is preserved across module reloads caused by HMR (Hot Module Replacement).
+  let globalWithMongo = global as typeof globalThis & {
+    _mongoClient?: MongoClient
+  }
+
+  if (!globalWithMongo._mongoClient) {
+    globalWithMongo._mongoClient = new MongoClient(uri, options)
+  }
+  client = globalWithMongo._mongoClient
+} else {
+  // In production mode, it's best to not use a global variable.
+  client = new MongoClient(uri, options)
+}
+
+// Export a module-scoped MongoClient. By doing this in a
+// separate module, the client can be shared across functions.
+export default client