fix(@angular-devkit/build-angular): remove unconditional CORS wildcard from webpack dev-server

The legacy webpack-based dev-server unconditionally sets
`Access-Control-Allow-Origin: *` on every response. This overrides
webpack-dev-server v5's cross-origin protections and leaves the local
dev server readable by any web page the developer visits in the same
browser session.

The modern `@angular/build` dev-server (Vite-based) already does not
set this header by default; its test contract explicitly asserts that
`Access-Control-Allow-Origin` is absent unless the user configures it.
This change brings the legacy webpack dev-server in line with that
contract.

Users who relied on the previous behavior can opt back in explicitly
via the existing `headers` option in `angular.json`:

  "serve": {
    "options": {
      "headers": { "Access-Control-Allow-Origin": "*" }
    }
  }

Author: Filbert Alfredo Saputro

packages/angular_devkit/build_angular/src/builders/dev-server/tests/options/headers_spec.ts

@@ -0,0 +1,65 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import { executeDevServer } from '../../index';
+import { executeOnceAndFetch } from '../execute-fetch';
+import { describeServeBuilder } from '../jasmine-helpers';
+import { BASE_OPTIONS, DEV_SERVER_BUILDER_INFO } from '../setup';
+
+describeServeBuilder(executeDevServer, DEV_SERVER_BUILDER_INFO, (harness, setupTarget) => {
+  describe('option: "headers"', () => {
+    beforeEach(async () => {
+      setupTarget(harness, {
+        styles: ['src/styles.css'],
+      });
+
+      // Application code is not needed for these tests
+      await harness.writeFile('src/main.ts', '');
+      await harness.writeFile('src/styles.css', '');
+    });
+
+    it('index response headers should include configured header', async () => {
+      harness.useTarget('serve', {
+        ...BASE_OPTIONS,
+        headers: {
+          'x-custom': 'foo',
+        },
+      });
+
+      const { result, response } = await executeOnceAndFetch(harness, '/');
+
+      expect(result?.success).toBeTrue();
+      expect(await response?.headers.get('x-custom')).toBe('foo');
+    });
+
+    it('should include configured Access-Control-Allow-Origin header', async () => {
+      harness.useTarget('serve', {
+        ...BASE_OPTIONS,
+        headers: {
+          'Access-Control-Allow-Origin': 'http://example.com',
+        },
+      });
+
+      const { result, response } = await executeOnceAndFetch(harness, '/main.js');
+
+      expect(result?.success).toBeTrue();
+      expect(await response?.headers.get('access-control-allow-origin')).toBe('http://example.com');
+    });
+
+    it('should not include Access-Control-Allow-Origin header by default', async () => {
+      harness.useTarget('serve', {
+        ...BASE_OPTIONS,
+      });
+
+      const { result, response } = await executeOnceAndFetch(harness, '/main.js');
+
+      expect(result?.success).toBeTrue();
+      expect(await response?.headers.has('access-control-allow-origin')).toBeFalse();
+    });
+  });
+});

packages/angular_devkit/build_angular/src/tools/webpack/configs/dev-server.ts

@@ -60,10 +60,7 @@ export async function getDevServerConfig(
     devServer: {
       host,
       port,
-      headers: {
-        'Access-Control-Allow-Origin': '*',
-        ...headers,
-      },
+      headers,
       historyApiFallback: !!index && {
         index: posix.join(servePath, getIndexOutputFile(index)),
         disableDotRule: true,