Kiosk Watchdog: A Tiny Chrome Extension for Abandoned Kiosk Sessions

We run a few self-service kiosks in our teaching labs. The flow is straightforward: a student walks up, swipes their card, gets bounced through SSO and MFA, and lands back on a kiosk page that lets them check out a hot plate or sign up for a lab section.

The flow breaks in one specific way that drove me crazy: a user starts the transaction, gets redirected to the SSO login page, realizes they don’t have their phone for the multi-factor prompt, and walks away. The browser is now stuck on a half-completed login screen tied to their university account. The next person who walks up sees that screen.

That is bad.

I went looking for an off-the-shelf fix. Existing kiosk-mode tools (Windows Assigned Access, Chrome’s kiosk flag, etc.) are great at locking down a browser, but none of them solve “the user got pulled out of the kiosk URL by an SSO redirect, and now we need to bounce them back home if they don’t finish in time.” That’s a much narrower problem, and the answer turned out to be a tiny browser extension.

What it does

Kiosk Watchdog is a ~150-line Manifest V3 Chrome extension. It does exactly one thing:

Two settings, both stored in chrome.storage.sync so they travel with a managed Google profile if you want them to:

• Kiosk URL — treated as a prefix. https://kiosk.example.org/app/ covers …/app/auth, …/app/scan, anything else under that path. Anything outside the prefix (your IdP, MFA provider, errant ad domain, whatever) counts as “off.”
• Timeout (seconds) — how long off-kiosk we’ll tolerate before yanking the session back home.

That’s it. Two inputs, one output.

How it works under the hood

The whole thing is a service worker that listens to three Chrome APIs:

chrome.tabs.onUpdated.addListener((tabId, changeInfo, tab) => {
  if (changeInfo.url || changeInfo.status === 'complete') {
    evaluateTab(tabId, tab.url);
  }
});

chrome.tabs.onActivated.addListener(/* ... */);
chrome.tabs.onRemoved.addListener(/* ... */);

When evaluateTab decides a tab is off-kiosk, it schedules a chrome.alarms alarm named after the tab ID:

const alarmName = (tabId) => `kiosk-reset-${tabId}`;

await chrome.alarms.create(alarmName(tabId), { delayInMinutes: timeoutSeconds / 60 });

When the alarm fires, the listener double-checks the tab is still off-kiosk (the user might have completed login since the alarm was set) and then redirects:

chrome.alarms.onAlarm.addListener(async (alarm) => {
  // ...
  const tab = await chrome.tabs.get(tabId);
  if (!isOnKiosk(tab.url, kioskUrl)) {
    await chrome.tabs.update(tabId, { url: kioskUrl });
  }
});

A few things matter here:

• chrome.alarms instead of setTimeout. Manifest V3 service workers can be killed by Chrome at any time. Alarms persist across kills. Timers don’t.
• Per-tab alarms, keyed on tabId. Avoids one tab’s timer cancelling another’s. Most kiosks run one tab, but I want the extension to be correct on the day someone opens a second.
• Re-check before yank. Race: alarm scheduled at T0, user finishes login at T+45s, alarm fires at T+60s. We check the current URL, not the URL we saw when scheduling, so completed logins don’t get bumped.
• Continuous off-kiosk time. When the user clicks through SSO → MFA → consent screen, each navigation is “off-kiosk” but chrome.alarms.create with the same name replaces the existing alarm. That means the timer counts continuous time off-kiosk, not per-page-load time. Tune your timeout to the worst-case real login (45–90 s for our flows).

Installation

Install it from the Chrome Web Store, or load it unpacked from the GitHub repo — both options are documented in the README.

For a lab fleet, the right move is Chrome Enterprise policy. The README has the recipe:

• ExtensionInstallForcelist to push the extension and pin its ID
• ExtensionSettings managed storage to pre-seed kioskUrl and timeoutSeconds so kiosks self-configure on first boot

Try it without a real kiosk

If you want to see it work before deploying, the README has a 4-step demo using example.com (which is IANA-reserved for exactly this kind of thing — RFC 2606). Set the kiosk URL to https://example.com/, set the timeout to 15 seconds, navigate the tab anywhere else, wait. The tab snaps back. No infrastructure, no test environment.

Source and license

• Repo: team-ward-labs/kiosk-watchdog
• License: MIT
• Manifest: V3 (the current standard; required for new submissions to the Chrome Web Store as of 2024)

If you run kiosks and have hit this same problem, give it a try. Issues and PRs welcome.