Large messaging platforms rarely collapse because authentication is broken. They collapse because authorization quietly expands, then stays expanded. The failure mode is not a single bug but a system property: credentials that were created for one narrow purpose become reusable, long-lived, and operationally too useful, until they function as capability grants far beyond the original intent.The industry has spent a decade hardening identity proofing and login defenses, yet incident reports keep circling back to the same operational reality: leaked tokens, misconfigured partner integrations, and automation scripts that inherit privileges no one remembers granting. What turns these common events into major incidents is blast radius. A single credential ends up authorizing too much surface area across assets, APIs, and workflows that were never meant to be coupled.