Why XSS Turns Tokens into Immediate Account Takeovers How HttpOnly Cookies Raise the Bar — Implementation and Tradeoffs Designing Refresh Token Flows: Rotation, Storage, and PKCE CSRF Defenses That Fit Cookie-Based Authentication Practical Implementation Checklist: code, headers, and server flows XSS doesn’t just break a page — it hands an attacker whatever your JavaScript can reach. Your browser storage choice turns that single bug into either a contained incident or a full account takeover. The symptoms you see in the field are predictable: stolen session tokens after an XSS bug, inconsistent cross-tab login state when teams move tokens between memory and localStorage , and brittle “silent refresh” flows that break when browsers tighten third‑party cookie policies. These are not abstract risks — they show up as support tickets, forced rollbacks, and emergency rotation when tokens leak.…