adopt to mongodb adapter changes

db/index.ts

@@ -5,16 +5,18 @@ import { BOOKING_STATUS } from './enums'
 
 let connectedPromise: Promise<mongoose.Mongoose>
 
+const MONGODB_OPTIONS = {
+  useCreateIndex: true,
+  useNewUrlParser: true,
+  useUnifiedTopology: true,
+}
+
 export function connect(): Promise<mongoose.Mongoose> {
   if (connectedPromise) {
     return connectedPromise
   }
 
-  connectedPromise = mongoose.connect(process.env.MONGO_URI, {
+  connectedPromise = mongoose.connect(process.env.MONGO_URI, MONGODB_OPTIONS)
-    useCreateIndex: true,
-    useNewUrlParser: true,
-    useUnifiedTopology: true,
-  })
 
   return connectedPromise
 }

pages/api/auth/[...nextauth].ts

@@ -5,13 +5,21 @@ import EmailProvider from "next-auth/providers/email"
 import { MongoDBAdapter } from "@next-auth/mongodb-adapter"
 import { connect } from "../../../db"
 import { Mongoose } from 'mongoose';
+import type { MongoClient } from "mongodb";
 
 let mongooseConnection: Mongoose;
 
+async function getMongoClient() {
+  const mongoose: Mongoose = await connect();
+
+  const mongoDatabase: unknown = mongoose.connection.db;
+  return mongoDatabase as MongoClient;
+}
+
 export default async function auth(req: NextApiRequest, res: NextApiResponse) {
   return await NextAuth(req, res, {
     secret: process.env.NEXTAUTH_SECRET,
-    adapter: MongoDBAdapter({ db: (await connect()).connection.db }),
+    adapter: MongoDBAdapter(getMongoClient()),
     providers: [
       EmailProvider({
         server: {