Next.js config redirect cache-control/headers

[flippidippi]

Goals

1. Permanent redirects can use Cache-Control header to tell browsers "how permanent" the 308 should be
2. Could still use Next.js config instead of having to do a work around
3. Could support any headers to set when doing a redirect (permanent or not)

Non-Goals

1. Redirects outside of Next.js config

Background

It would make the redirect config in Next.js more flexible and not require work arounds.

Proposal

Allow sets a header key on a Next.js config Redirect in addition to the existing source, destination, permanent, etc.

This would allow devs to set stuff like Cache-Control to tell browsers how long a permanent redirect should be cached for.

[flippidippi]

Another way to do this would be to instead of doing resHeaders: null for when there's a redirect, we just return resHeaders.
This is way less straight forward but it would allow devs to target the same places as the redirects to set the headers.

https://github.com/vercel/next.js/blob/canary/packages/next/src/server/lib/router-utils/resolve-routes.ts#L836

Might look something like this in a user's config if they want to do this

    async headers () {
      const existingHeaders = await config.headers?.() ?? []
      const permanentRedirectHeaders = getUrlRedirects()
        .filter((redirect) => redirect.permanent === true)
        .map(({ destination, permanent, ...redirect }) => ({
          ...redirect,
          headers: [
            { key: 'Cache-Control', value: 'private, max-age=86400' }
          ]
        }))

      return [...existingHeaders, ...permanentRedirectHeaders]
    }