Add support for middleware rewrite proxy headers

[johnsardine]

Describe the feature you'd like to request

I would like to be able to specify headers to be sent by the proxy that is running behind the NextResponse.rewrite middleware response.

I understand it's possible to set headers in the NextResponse.rewrite response, but these headers are sent to the user visiting the next.js page, what I would like is to set headers that the destination server will receive.

Upon digging into the next.js internals, I understand we'd need to provide such headers in the Proxy instance within proxyRequest inside /packages/next/server/base-server.ts

Describe the solution you'd like

I would like to be able to, perhaps, provide a config object as second parameter of NextResponse.rewrite which could accept something like forwardHeaders that accepts a Headers object and this would then be merged with the headers that the proxy may already need to send.

Describe alternatives you've considered

Currently, my alternative solution is preform this rewrite using nginx and provide the headers there. If these headers can be forwarded within nextjs, I believe this feature will be even more powerful.

[johnsardine]

It appears this would fix the problem raised in this discussion #31188

[manoj-mukherjee-maersk]

any solution? Are we supporting nextjs middleware as http-proxy?

[icyJoseph]

Gonna have to vouch for this one as well.

[JoshBarr]

I've also run into this limitation. I've raised a PR: #35093

[yoniheib]

Would be great if this was supported. I'd also like to proxy an authorization header to the destination without exposing it to the client.

[m4rvr]

Any update on this?

[audriuiv]

Any updates?