Forwarding headers

[AndreaCrotti]

I have to do something that I thought would be simple, but (probably also because I'm not a JS dev), I'm really struggling to make work.
We use the supergraph handler, and our meshrc.yaml config looks like this:

serve:
  browser: false
  endpoint: '/v1/graphql'
  fork: false
  port: 8080

sources:
  - name: 'supergraph'
    handler:
      supergraph:
        source: './supergraph.graphql'

additionalEnvelopPlugins: './lib/envelopPlugins'
logger: './lib/logger'

We have some plugins already to manipulate the request/response, however what I actually need now is a simple plugin that takes a set of allowed headers, loops over the headers in the response currently and if it's allowed actually send it back to the client in the actual response.

function useForwardResponseHeaders(allowedResponseHeaders: Set<string>): MeshPlugin<RequestContext> {
	return {
		onFetch(onFetchArgs: OnFetchHookPayload<RequestContext>) {

			return function onFetchDone({ response }) {};
		},
	};

The problem I'm having is that I can never find a way to have both the headers from the original response and be able to modify the response going out at the same time, what magic incantation do I need to use to do that?
Also, it seems like something that should be available as plugin already, isn't there something I can reuse?
Thanks

[vik-osteon]

Hi there, upvoting this question as very relevant. I'm having a Mesh v0 served as a /graphql route by express.js and I'm trying to find a way to ensure that after request gets into Mesh the custom headers set by express middleware make it to the actual API host (which does not seem to happen atm).
What would be a recommended approach here? should I look into custom Envelop plugins, or..?

Any advice would be much appreciated.