fix: localKubectlProxy auth provider throwing error (#17139)

* fix: localKubectlProxy auth provider throwing error

Signed-off-by: Matthew Clarke <mclarke@spotify.com>

* docs: changeset

Signed-off-by: Matthew Clarke <mclarke@spotify.com>

---------

Signed-off-by: Matthew Clarke <mclarke@spotify.com>

.changeset/poor-cars-fold.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-kubernetes-backend': patch
+---
+
+fix localKubectlProxy auth provider fetching

plugins/kubernetes-backend/src/service/KubernetesFetcher.test.ts

@@ -235,6 +235,55 @@ describe('KubernetesFetcher', () => {
         ],
       });
     });
+    it('localKubectlProxy authProvider fetches resources correctly', async () => {
+      worker.use(
+        rest.get(
+          'http://localhost:9999/k8s/clusters/1234/api/v1/services',
+          (req, res, ctx) =>
+            res(
+              withLabels(req, ctx, {
+                items: [{ metadata: { name: 'service-name' } }],
+              }),
+            ),
+        ),
+      );
+
+      const result = await sut.fetchObjectsForService({
+        serviceId: 'some-service',
+        clusterDetails: {
+          name: 'cluster1',
+          url: 'http://localhost:9999/k8s/clusters/1234',
+          authProvider: 'localKubectlProxy',
+        },
+        objectTypesToFetch: new Set([
+          {
+            group: '',
+            apiVersion: 'v1',
+            plural: 'services',
+            objectType: 'services',
+          },
+        ]),
+        labelSelector: '',
+        customResources: [],
+      });
+
+      expect(result).toStrictEqual({
+        errors: [],
+        responses: [
+          {
+            type: 'services',
+            resources: [
+              {
+                metadata: {
+                  name: 'service-name',
+                  labels: { 'backstage.io/kubernetes-id': 'some-service' },
+                },
+              },
+            ],
+          },
+        ],
+      });
+    });
     it('should return pods, services', async () => {
       worker.use(
         rest.get('http://localhost:9999/api/v1/pods', (req, res, ctx) =>

plugins/kubernetes-backend/src/service/KubernetesFetcher.ts

@@ -191,7 +191,10 @@ export class KubernetesClientBasedFetcher implements KubernetesFetcher {
 
     let url: URL;
     let requestInit: RequestInit;
-    if (clusterDetails.serviceAccountToken) {
+    if (
+      clusterDetails.serviceAccountToken ||
+      clusterDetails.authProvider === 'localKubectlProxy'
+    ) {
       [url, requestInit] = this.fetchArgsFromClusterDetails(clusterDetails);
     } else if (fs.pathExistsSync(Config.SERVICEACCOUNT_TOKEN_PATH)) {
       [url, requestInit] = this.fetchArgsInCluster();