feat(common): on-by-default XSRF support in HttpClient (#18108)

Fixes #18100

packages/common/src/cookie.ts

@@ -0,0 +1,20 @@
+/**
+ * @license
+ * Copyright Google Inc. 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.io/license
+ */
+
+export function parseCookieValue(cookieStr: string, name: string): string|null {
+  name = encodeURIComponent(name);
+  for (const cookie of cookieStr.split(';')) {
+    const eqIndex = cookie.indexOf('=');
+    const [cookieName, cookieValue]: string[] =
+        eqIndex == -1 ? [cookie, ''] : [cookie.slice(0, eqIndex), cookie.slice(eqIndex + 1)];
+    if (cookieName.trim() === name) {
+      return decodeURIComponent(cookieValue);
+    }
+  }
+  return null;
+}