Credentials Provider

The Credentials provider allows you to handle signing in with arbitrary credentials, such as a username and password, domain, two factor authentication or hardware device (e.g. YubiKey U2F / FIDO).

It is intended to support use cases where you have an existing system you need to authenticate users against, and therefore users authenticated in this manner are not persisted in the database.

Resources

Client-side Input Validation Example

Configuration

/auth.ts

import NextAuth from "next-auth"
import Credentials from "next-auth/providers/credentials"
 
export const { signIn, signOut, auth } = NextAuth({
  providers: [
    Credentials({
      credentials: {
        username: { label: "Username" },
        password: { label: "Password", type: "password" },
      },
      async authorize({ request }) {
        const response = await fetch(request)
        if (!response.ok) return null
        return (await response.json()) ?? null
      },
    }),
  ],
})

/src/auth.ts

import { SvelteKitAuth } from "@auth/sveltekit"
import Credentials from "@auth/sveltekit/providers/credentials"
 
export const { handle, signIn, signOut } = SvelteKitAuth({
  providers: [
    Credentials({
      credentials: {
        username: { label: "Username" },
        password: { label: "Password", type: "password" },
      },
      async authorize({ request }) {
        const response = await fetch(request)
        if (!response.ok) return null
        return (await response.json()) ?? null
      },
    }),
  ],
})

/src/app.ts

import { ExpressAuth } from "@auth/express";
import Credentials from "@auth/express/providers/credentials";
 
app.use("/auth/*", ExpressAuth({
  providers: [
    Credentials({
      credentials: {
        username: { label: "Username" },
        password: { label: "Password", type: "password" },
      },
      async authorize({ request }) {
        const response = await fetch(request);
        if (!response.ok) return null;
        return (await response.json()) ?? null;
      },
    }),
  ],
});

Custom Error Messages

You can throw a custom error in the authorize function to return a custom error message to the user.

@/auth.ts

import NextAuth, { CredentialsSignin } from "next-auth"
import Credentials from "next-auth/providers/credentials"
 
class InvalidLoginError extends CredentialsSignin {
  code = "Invalid identifier or password"
}
 
export const { handlers, auth } = NextAuth({
  providers: [
    Credentials({
      credentials: {
        username: { label: "Username" },
        password: { label: "Password", type: "password" },
      },
      async authorize(credentials) {
        throw new InvalidLoginError()
      },
    }),
  ],
})

You will then receive that custom error code in the query parameters of the signin page your user returns to after a failed login attempt, for example https://app.company.com/auth/signin?error=CredentialsSignin&code=Invalid+identifier+or+password.

⚠️

OAuth providers spend significant amounts of money, time, and engineering effort to build:

abuse detection (bot-protection, rate-limiting)
password management (password reset, credential stuffing, rotation)
data security (encryption/salting, strength validation)

and much more for authentication solutions. It is likely that your application would benefit from leveraging these battle-tested solutions rather than try to rebuild them from scratch.

If you’d still like to build password-based authentication for your application despite these risks, Auth.js gives you full control to do so.

Coinbase Descope

Credentials Provider

Resources

Configuration

Custom Error Messages

About Auth.js

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Acknowledgements