Custom sign-in form for email magic link provider doesn't work

[AndrewRayCode]

I'm trying to implement an ajax form for magic-link-email sign-in, where the user enters their email and they're emailed either a sign-up or log-in link based on if they have an account.

From a UX perspective, the way this should work is the user should enter their email into an input box, click a button, get a loading spinner, and without any redirects, get a message like "your magic email link is on the way." They should not be redirected to a separate sign-in page, which doesn't make sense for magic email links.

According to https://next-auth.js.org/configuration/pages#email-sign-in you can submit to /api/auth/signin/email:

    <form method="post" action="/api/auth/signin/email">
      <input name="csrfToken" type="hidden" defaultValue={csrfToken} />
      <label>
        Email address
        <input type="email" id="email" name="email" />
      </label>
      <button type="submit">Sign in with Email</button>
    </form>

However, when I instrument this on my page, and submit the form via an ajax POST with a json body, something like post('/api/auth/signin/email', { email }) (form encoded), it returns a redirect to http://localhost
/api/auth/signin?csrf=true, which dies with ERR_CONNECTION_REFUSED

Is it possible to instrument this via ajax to avoid a separate "sign in" page via email? Was the EmailProvider overlooked compared to the other sign-in UX flows? Or (more likely) am I missing something obvious?

Also, the docs say this:

You can also use the signIn() function which will handle obtaining the CSRF token for you:

Which doesn't make sense. What does this mean? How does this relate to submitting the form? Do you call signIn() while intercepting the form submit?