Why traditional sessions fail at global scale and how Senior Engineers design resilient, JWT-based authentication for Fintech. Most Android engineers are proficient at building login screens. You take user credentials, pass them to a  /login  endpoint, receive a token, and move on. However, transitioning to an  Android authentication architecture  that supports  5 million+ users  — particularly in fintech — requires a fundamental shift. At this scale, even a 50ms cross-region lookup can compound into seconds of perceived latency across multiple API calls. The challenge isn’t the UI; it’s resilience, global latency, and cryptographic trust. This is Part 1 of our 9-part “Scaling Secure Android” series. We are moving beyond basic tutorials into Senior-level system design. 🛑 The Core Problem: Why Stateful Sessions Fail at Scale In a traditional “stateful” architecture, the authentication “state” lives on the server. The server creates a session ID, store...