return null in CredentialsProvider redirects to /api/auth/error

[zakaryan2004]

According to the documentations, writing return null in the authorize callback of the CredentialsProvider should show the user this text: "Sign in failed. Check the details you provided are correct.". In v3, this is the case.

But, in v4, if the authorize callback returns null, the user is then redirected to this URL:
http://localhost:3000/api/auth/error?error=CredentialsSignin?provider=credentials

Navigating to this URL shows the correct text in the intended way:
http://localhost:3000/api/auth/signin?error=CredentialsSignin?provider=credentials

How to test this:

1. Clone the next-auth-example v4 branch and get it running.
2. (optional) Remove all other providers
3. Add CredentialsProvider

CredentialsProvider({
  id: 'credentials',
  name: 'Credentials',
  credentials: {
    username: { label: "Username", type: "text" },
    password: { label: "Password", type: "password" }
  },
  authorize: async (credentials, req) => {
    return null
  }
}),

4. Navigate to the Sign in page and try to sign in.
5. Notice the /api/auth/error page instead of /api/auth/signin

You can test the same thing with the main branch of next-auth-example (with minor changes in provider), and notice this feature working correctly.

I think this should be an Issue, but I made it a discussion as I may not be aware of changes made in v4 which achieve this in other ways. In any case, I think it should work the same way as it does on v3, without anything additional.

I have taken a small look at the source code but didn't find the root cause yet.

[zakaryan2004]

Nevermind, this is solved in beta.7. It's so amusing how many times one can spend fixing a problem, and then find the fix immediately after writing about the problem, especially to other people.