[Feature Request] get headers from client signIn response.

[jcyuan]

Goals

better to have an interface to allow api fetching customizable

Non-Goals

No response

Background

on my server side, i have a rate-limiter which will block auth apis from requesting too fast (middleware layer), when it takes effect, it will directly respond with status error & some simple text (not json), this response will be received by the signIn method (it uses fetch) which will cause data.json() error.
btw, i need to know some header values fetched by signIn method but there is no way to get it because the request was wrapped in the signIn method.

Proposal

add an new option into the NextAuthOptions, something like
"apiClient": axios.create(),
and then in signIn method (or where sends requests):
(options.apiClient || fetch).doRequest...