feat: add helper methods for auth cookie headers

introduced `getAuthCookieHeader` and `removeAuthCookieHeader` methods to simplify header management for authentication cookies. added tests to validate the new methods.

app/__test__/auth/Authenticator.spec.ts

@@ -1,3 +1,41 @@
+import { Authenticator } from "auth/authenticate/Authenticator";
 import { describe, expect, test } from "bun:test";
 
-describe("Authenticator", async () => {});
+describe("Authenticator", async () => {
+   test("should return auth cookie headers", async () => {
+      const auth = new Authenticator({}, null as any, {
+         jwt: {
+            secret: "secret",
+            fields: [],
+         },
+         cookie: {
+            sameSite: "strict",
+         },
+      });
+      const headers = await auth.getAuthCookieHeader("token");
+      const cookie = headers.get("Set-Cookie");
+      expect(cookie).toStartWith("auth=");
+      expect(cookie).toEndWith("HttpOnly; Secure; SameSite=Strict");
+
+      // now expect it to be removed
+      const headers2 = await auth.removeAuthCookieHeader(headers);
+      const cookie2 = headers2.get("Set-Cookie");
+      expect(cookie2).toStartWith("auth=; Max-Age=0; Path=/; Expires=");
+      expect(cookie2).toEndWith("HttpOnly; Secure; SameSite=Strict");
+   });
+
+   test("should return auth cookie string", async () => {
+      const auth = new Authenticator({}, null as any, {
+         jwt: {
+            secret: "secret",
+            fields: [],
+         },
+         cookie: {
+            sameSite: "strict",
+         },
+      });
+      const cookie = await auth.unsafeGetAuthCookie("token");
+      expect(cookie).toStartWith("auth=");
+      expect(cookie).toEndWith("HttpOnly; Secure; SameSite=Strict");
+   });
+});