feat: add timezone-aware TOTP time travel

tests/components/workbench.test.tsx

@@ -1,4 +1,10 @@
-import { render, screen } from "@testing-library/react";
+import {
+  fireEvent,
+  render,
+  screen,
+  waitFor,
+  within,
+} from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { describe, expect, it } from "vitest";
 import { Workbench } from "../../src/components/Workbench";
@@ -38,4 +44,46 @@ describe("authentication workbench", () => {
       screen.getByRole("button", { name: "Create test credential" }),
     ).toBeDisabled();
   });
+
+  it("generates a TOTP at an absolute wall-clock time in an explicit timezone", async () => {
+    const user = userEvent.setup();
+    render(<Workbench />);
+
+    fireEvent.change(screen.getByLabelText("Base32 secret"), {
+      target: { value: "GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ" },
+    });
+    fireEvent.change(screen.getByLabelText("Account"), {
+      target: { value: "rfc-vector" },
+    });
+    await user.click(screen.getByRole("button", { name: "Show secret" }));
+    await waitFor(() =>
+      expect(
+        (screen.getByLabelText("Provisioning URI") as HTMLTextAreaElement)
+          .value,
+      ).toContain("secret=GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ"),
+    );
+    await user.selectOptions(screen.getByLabelText("Digits"), "8");
+    await user.click(screen.getByRole("button", { name: "Point in time" }));
+    fireEvent.change(screen.getByLabelText("Local date and time"), {
+      target: { value: "1970-01-01T00:00:59" },
+    });
+    fireEvent.change(screen.getByLabelText("IANA timezone"), {
+      target: { value: "UTC" },
+    });
+
+    expect(screen.getByLabelText("Local date and time")).toHaveValue(
+      "1970-01-01T00:00:59.000",
+    );
+    expect(screen.getByLabelText("IANA timezone")).toHaveValue("UTC");
+    expect(screen.queryByRole("alert")).not.toBeInTheDocument();
+    expect(screen.getByText("1970-01-01T00:00:59.000Z")).toBeInTheDocument();
+    expect(
+      within(screen.getByText("TOTP counter").parentElement!).getByText("1"),
+    ).toBeInTheDocument();
+    await waitFor(() =>
+      expect(document.querySelector(".code-display")).toHaveTextContent(
+        "942 870 82",
+      ),
+    );
+  });
 });