How I Smashed a Bug in a Shared Authentication Library
This is a submission for DEV's Summer Bug Smash: Smash Stories powered by Sentry . This happened a while ago at one of the corporations where I worked. I was working on a web application as a full-stack developer, so I was responsible for both the frontend and the backend. Because the corporation was huge, there were several libraries and services shared across multiple teams and maintained by…
This account narrates a developer's experience with a bug in a shared authentication library during a corporate project. After the initial release, users reported that opening the web application in multiple tabs caused authentication to fail intermittently. As the senior developer, the reporter took the lead in investigating the issue.
They discovered that the frontend authentication library, sent an invalidated refresh token to the backend when the user tried to refresh the authentication token, causing a race condition between multiple tabs. This led to the backend returning a 403 Forbidden response, and the frontend would then break, requiring a page refresh or closing to recover.
After several discussions with the frontend and backend teams, they could not agree on the responsibility for the bug. The frontend team claimed the backend was not supposed to return a 403 Forbidden response, while the backend team believed the frontend was sending an invalidated refresh token. Despite repeated attempts to resolve the issue, they were unable to reproduce the problem, and the frontend team suggested users should not open the application in multiple tabs.
Eventually, the reporter took matters into their own hands, arranging a meeting with all involved parties and convincing them that the frontend authentication library was responsible for the bug. They removed the corporate library from the project and reimplemented the client-side authentication flow directly against the existing authentication service.
The reporter addressed the issue by updating the Angular HTTP interceptor and the token refresh flow, handling authentication-related responses, including 403 Forbidden, without causing the entire tab to become unresponsive. They also reworked the handling of invalidated tokens and failed refresh attempts, preventing the authentication flow from stopping completely.
After implementing these changes, the bug was resolved, and the developer outlined the improvements and fixes in their Bug Smash story, emphasizing how fixing one bug led to rewriting the entire feature due to the corporate nature of the authentication library.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
