next-auth error: 'Adapter' is not assignable to type 'Adapter | undefined'

Question

I'm following this documentation: https://authjs.dev/reference/adapter/mongodb to use next-auth. This is the relevant code:

import NextAuth from "next-auth"
import { MongoDBAdapter } from "@auth/mongodb-adapter"
import clientPromise from "../../../lib/mongodb"

...

export default NextAuth({
    providers,
    adapter: MongoDBAdapter(clientPromise),
})

I get the following error, which makes no sense to me:

Type 'Adapter' is not assignable to type 'Adapter | undefined'.
  Type 'Adapter' is not assignable to type 'DefaultAdapter & { createVerificationToken: (verificationToken: VerificationToken) => Awaitable<VerificationToken | null | undefined>; useVerificationToken: (params: { ...; }) => Awaitable<...>; }'.
    Type 'Adapter' is not assignable to type 'DefaultAdapter'.
      Types of property 'createUser' are incompatible.
        Type '((user: Omit<AdapterUser, "id">) => Awaitable<AdapterUser>) | undefined' is not assignable to type '(user: Omit<AdapterUser, "id">) => Awaitable<AdapterUser>'.
          Type 'undefined' is not assignable to type '(user: Omit<AdapterUser, "id">) => Awaitable<AdapterUser>'.ts(2322)
types.d.ts(106, 5): The expected type comes from property 'adapter' which is declared here on type 'AuthOptions'
(property) AuthOptions.adapter?: Adapter | undefined
You can use the adapter option to pass in your database adapter.

Required: No

Answer 1

I ran into the same issue today. I was importing MongoDBAdapter from @auth/mongodb-adapter, but actually needed to import from the next-auth adapter.

I ran:

npm install @next-auth/mongodb-adapter

Then changed my import to:

import { MongoDBAdapter } from "@next-auth/mongodb-adapter";

I have no clue what the actual issue is, just that installing the right adapter and changing the import fixed it for me.

Hope this helps!

Answer 2

I got the same type error with @auth/firebase-adapter.

ype error: Type 'Adapter' is not assignable to type 'Adapter | undefined'.
  Type 'Adapter' is not assignable to type 'DefaultAdapter & { createVerificationToken: (verificationToken: VerificationToken) => Awaitable<VerificationToken | null | undefined>; useVerificationToken: (params: { ...; }) => Awaitable<...>; }'.
    Type 'Adapter' is not assignable to type 'DefaultAdapter'.
      Types of property 'createUser' are incompatible.
        Type '((user: Omit<AdapterUser, "id">) => Awaitable<AdapterUser>) | undefined' is not assignable to type '(user: Omit<AdapterUser, "id">) => Awaitable<AdapterUser>'.
          Type 'undefined' is not assignable to type '(user: Omit<AdapterUser, "id">) => Awaitable<AdapterUser>'

First, import type Adapter from next-auth/adapters.

import type { Adapter } from "next-auth/adapters";

and change NextAuthOptions.

import type { Adapter } from "next-auth/adapters";

export const authOptions: NextAuthOptions = {,
  adapter: FirestoreAdapter(firestore) as Adapter,
  ...
};