Add callbackUrl field to credentials signin form

[jjonescz]

☕️ Reasoning

The bug:

1. Visit the signin page with a callback URL (e.g., /auth/signin?callbackUrl=/test).
2. In parallel visit another URL which also redirects to sign in (e.g. the browser automatically requests /favicon.ico and is redirected to /auth/signin?callbackUrl=/favicon.ico which saves /favicon.ico into callbackUrl cookie).
3. Now fill in credentials and sign into the first page - it redirects to /favicon.ico instead of /test. That's because the callbackUrl from the query string is lost for the credentials provider (this PR should fix that) and the cookie is used instead.

🧢 Checklist

• Documentation
• Tests
• Ready to be merged

🎫 Affected issues

📌 Resources

• Security guidelines
• Contributing guidelines
• Code of conduct
• Contributing to Open Source

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
auth-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 17, 2023 2:47pm

1 Ignored Deployment

Name	Status	Preview	Comments	Updated (UTC)
next-auth-docs	⬜️ Ignored (Inspect)	Visit Preview		Oct 17, 2023 2:47pm

[vercel]

@jjonescz is attempting to deploy a commit to the authjs Team on Vercel.

A member of the Team first needs to authorize it.

[ThangHuuVu]

@jjonescz hey sorry for the late reply, I'm not able to reproduce this using our deployed example: https://next-auth-example.vercel.app/auth/signin?callbackUrl=/favicon.ico

Could you open an issue first with a minimal reproducible example? I'm going to close this in the meantime to reduce maintaining overhead