[HTTP] Add build number to headers so that we can identify UIs (#163577)

Close https://github.com/elastic/kibana/issues/162332

### List

- [x] Add E2E test

---------

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

packages/core/http/core-http-browser-internal/src/fetch.test.ts

@@ -29,6 +29,7 @@ describe('Fetch', () => {
   const fetchInstance = new Fetch({
     basePath: new BasePath(BASE_PATH),
     kibanaVersion: 'VERSION',
+    buildNumber: 1234,
     executionContext: executionContextMock,
   });
   afterEach(() => {
@@ -160,6 +161,7 @@ describe('Fetch', () => {
       expect(fetchMock.lastOptions()!.headers).toMatchObject({
         'content-type': 'application/json',
         'kbn-version': 'VERSION',
+        'kbn-build-number': '1234',
         'x-elastic-internal-origin': 'Kibana',
         myheader: 'foo',
       });
@@ -178,6 +180,19 @@ describe('Fetch', () => {
         `"Invalid fetch headers, headers beginning with \\"kbn-\\" are not allowed: [kbn-version]"`
       );
     });
+    it('should not allow overwriting of kbn-build-number header', async () => {
+      fetchMock.get('*', {});
+      await expect(
+        fetchInstance.fetch('/my/path', {
+          headers: {
+            myHeader: 'foo',
+            'kbn-build-number': 4321,
+          },
+        })
+      ).rejects.toThrowErrorMatchingInlineSnapshot(
+        `"Invalid fetch headers, headers beginning with \\"kbn-\\" are not allowed: [kbn-build-number]"`
+      );
+    });
 
     it('should not allow overwriting of x-elastic-internal-origin header', async () => {
       fetchMock.get('*', {});

packages/core/http/core-http-browser-internal/src/fetch.ts

@@ -31,6 +31,7 @@ import { HttpInterceptHaltError } from './http_intercept_halt_error';
 interface Params {
   basePath: IBasePath;
   kibanaVersion: string;
+  buildNumber: number;
   executionContext: ExecutionContextSetup;
 }
 
@@ -135,6 +136,7 @@ export class Fetch {
         'Content-Type': 'application/json',
         ...options.headers,
         'kbn-version': this.params.kibanaVersion,
+        'kbn-build-number': this.params.buildNumber,
         [ELASTIC_HTTP_VERSION_HEADER]: version,
         [X_ELASTIC_INTERNAL_ORIGIN_REQUEST]: 'Kibana',
         ...(!isEmpty(context) ? new ExecutionContextContainer(context).toHeader() : {}),

packages/core/http/core-http-browser-internal/src/http_service.ts

@@ -31,13 +31,14 @@ export class HttpService implements CoreService<HttpSetup, HttpStart> {
 
   public setup({ injectedMetadata, fatalErrors, executionContext }: HttpDeps): HttpSetup {
     const kibanaVersion = injectedMetadata.getKibanaVersion();
+    const buildNumber = injectedMetadata.getKibanaBuildNumber();
     const basePath = new BasePath(
       injectedMetadata.getBasePath(),
       injectedMetadata.getServerBasePath(),
       injectedMetadata.getPublicBaseUrl()
     );
 
-    const fetchService = new Fetch({ basePath, kibanaVersion, executionContext });
+    const fetchService = new Fetch({ basePath, kibanaVersion, buildNumber, executionContext });
     const loadingCount = this.loadingCount.setup({ fatalErrors });
     loadingCount.addLoadingCountSource(fetchService.getRequestCount$());
 

test/plugin_functional/plugins/core_http/server/plugin.ts

@@ -22,6 +22,15 @@ export class CoreHttpPlugin implements Plugin {
         return res.ok();
       }
     );
+    router.get(
+      {
+        path: '/api/core_http/headers',
+        validate: false,
+      },
+      async (ctx, req, res) => {
+        return res.ok({ body: req.headers });
+      }
+    );
   }
 
   public start() {}

test/plugin_functional/test_suites/core_plugins/http.ts

@@ -7,6 +7,7 @@
  */
 
 import expect from '@kbn/expect';
+import SemVer from 'semver';
 import { PluginFunctionalProviderContext } from '../../services';
 
 export default function ({ getService, getPageObjects }: PluginFunctionalProviderContext) {
@@ -29,5 +30,22 @@ export default function ({ getService, getPageObjects }: PluginFunctionalProvide
       const canceledErrorName = await getCancelationErrorName();
       expect(canceledErrorName).to.eql('AbortError');
     });
+
+    it('sets the expected headers', async () => {
+      const headers = await browser.executeAsync<Record<string, string>>(async (cb) => {
+        cb(await window._coreProvider.setup.core.http.get('/api/core_http/headers'));
+      });
+      expect(headers).to.have.property('kbn-version');
+      expect(!!SemVer.valid(headers['kbn-version'])).to.be(true);
+
+      expect(headers).to.have.property('kbn-build-number');
+      expect(headers['kbn-build-number']).to.match(/^\d+$/);
+
+      expect(headers).to.have.property('x-elastic-internal-origin');
+      expect(headers['x-elastic-internal-origin']).to.be.a('string');
+
+      expect(headers).to.have.property('x-kbn-context');
+      expect(headers['x-kbn-context']).to.be.a('string');
+    });
   });
 }