[CatalogClient] extra headers in Catalog request

[alde]

Allow the setting of custom extra headers in CatalogRequestOptions.

Use-case: Passing in information from the front-end or another backend service for example for logging request information (like identity, correlation-id, etc.).

Hey, I just made a Pull Request!

✔️ Checklist

• A changeset describing the change and affected packages. (more info)
• Added or updated documentation
• Tests for new functionality and regression tests for bug fixes
• Screenshots attached (for UI changes)
• All your commits have a Signed-off-by line in the message. (more info)

[backstage-goalie]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@backstage/catalog-client	packages/catalog-client	minor	v1.4.6

[camilaibs]

LGTM

[github-actions]

Uffizzi Ephemeral Environment - Virtual Cluster

Your cluster pr-21324 was successfully created. Learn more about Uffizzi virtual clusters
To connect to this cluster, follow these steps:

1. Download and install the Uffizzi CLI from https://docs.uffizzi.com/install
2. Login to Uffizzi, then select the backstage account and project:

uffizzi login

Select an account: 
  ‣ backstage
    jdoe

Select a project or create a new project: 
  ‣ backstage-6783521

3. Update your kubeconfig: uffizzi cluster update-kubeconfig pr-21324 --kubeconfig=[PATH_TO_KUBECONFIG]
   After updating your kubeconfig, you can manage your cluster with kubectl, kustomize, helm, and other tools that use kubeconfig files: kubectl get namespace --kubeconfig [PATH_TO_KUBECONFIG]

Access the backstage endpoint at https://backstage-default-pr-21324-c1959.uclusters.app.uffizzi.com

[github-actions]

Uffizzi Cluster pr-21324 was deleted.

[Rugvip]

I believe you can already do this by decorating the fetch API before passing it to the catalog client. You should be able to use createFetchApi to help out with the wrapping of the existing fetch as well:

backstage/packages/core-app-api/src/apis/implementations/FetchApi/createFetchApi.ts

Line 32 in 6b037c6

export function createFetchApi(options: {

[alde]

@Rugvip I spent some time to look into that, and I'm not at all sure how to do it modifying the fetchApi with a middleware without making the code really complicated instead of just passing it on the call that already has support for (very limited) options

[freben]

Hm the examples are identity and correlation-ID - at least the second of those is a per-request thing right?

Identity in the form of specifically the Backstage token should be injected automatically by the fetchApi as long as it's been passed to the client in the first place - which it is by default.

[Rugvip]

Realized there's no need for using createFetchApi, it's possible, but just adds a bit more code. Anyway, here's an example of how to add a totally random correlation ID to all requests:

createApiFactory({
  api: catalogApiRef,
  deps: {
    discoveryApi: discoveryApiRef,
    fetchApi: fetchApiRef,
  },
  factory: ({ discoveryApi, fetchApi: { fetch: innerFetch } }) =>
    new CatalogClient({
      discoveryApi,
      fetchApi: {
        fetch: async (input, init) => {
          const request = new Request(input as any, init);
          request.headers.set('correlation-id', '4');
          return innerFetch(request);
        },
      },
    }),
}),

[alde]

@Rugvip The problem that I'm trying to solve is setting it to a different thing in each call to forward headers from an incoming call for example

const headerFromUpstream = request.headers['x-tracing-id'];
catalogApi.getLocationById(locationId, { headers: { 'x-tracing-id': headerFromUpstream } });

[Rugvip]

I noted this down in #15999 so that we can at very least try to tackle this as part of broader service auth/protected by default work. Also noted that the particular problem of forwarding information from an incoming request to outgoing ones is something that could potentially be solved by context/thread local storage, which is something we might explore again as part of that work.