Add dynamic url for login redirect

[stinkymonkeyph]

Goals

1. Allow configuration for dynamic hostname without relying solely on NEXTAUTH_URL, because sometimes deployment requires a way to set NEXTAUTH_URL based on deployment conditions, for example, netlify deploy previews relying solely on ENV is cumbersome so we need a way to set it up dynamically

Non-Goals

No response

Background

Current setup only allows NEXTAUTH_URL to be set beforehand, this is good when you know your domain already but what if we are to integrate a CI/CD with dynamic hostname for the instance?

Netlify offers a deploy preview where a PR can be deployed for testing, where NEXTAUTH_URL needs to be dynamic.

Proposal

Find a way to dynamically detect or set origin/host url without relying solely on NEXTAUTH_URL

P.S. I am interested in contributing with guidance

[stinkymonkeyph]

Similar discussion: #9785