How a BFF Layer Cut 52 API Requests to One and Caught a Data Leak

A development team replaced direct browser-to-backend API calls with a Backend-for-Frontend (BFF) layer after a bills worklist page was generating 52 network requests and loading nearly 10,000 rows into the browser just to display one paginated screen. The BFF, built as a set of resource routes on an existing Express server, consolidates permission checks, server-side filtering, sorting, and pagination into a single endpoint per screen. Three months after implementation, the layer handles 80 routes across 9 features and has meaningfully reduced client-side processing. During rollout, the team discovered two caching vulnerabilities: a browser cache misconfiguration briefly exposed one user's data to another, fixed by adding a Vary: Cookie header, and an in-memory server cache risked cross-tenant data leaks until it was strictly keyed by user ID. The experience led the team to treat every cache header as a security setting and enforce tenant scoping from auth tokens rather than query parameters.