When an API Key Lives in Local Storage: A Subtle but Risky Pattern

While testing a production web application, I noticed a third-party API key (used for consent and privacy management) stored directly in the browser’s localStorage . It’s a common pattern in modern frontends—but one that can quietly expand your attack surface. This post breaks down why it matters, how it can be abused in real scenarios, and what both developers and bug hunters should look for. What Happened A consent-management service API key was present in localStorage on page load (no authent