Hi everyone! I’ve been experimenting with session handling and cookie‑based authentication from a defensive/security testing standpoint. In the past, copying and importing cookie data (for example via browser tools or extensions) between accounts sometimes allowed a session to be reused. This behavior worked for a while, but no longer does.

Previously, I built a small tool to analyze session identifiers present in cookies for research purposes, mainly to understand how session invalidation, binding, and rotation were implemented. I’d typically export cookies in JSON format and observe how modern platforms handled them when environments or accounts changed.

Now that this approach no longer works, I’m trying to understand what changes were introduced on the security side—for example, whether it’s due to stricter session binding, device fingerprinting, token rotation, SameSite/HttpOnly flags, or server‑side validation improvements.

Does anyone have insight into which defensive mechanisms are now preventing session reuse, or what best practices platforms currently use to mitigate this class of issue? And also, if you know this thing can be bypassed, let me know.