Session variables was exist in Traditional web, but in reactive web app there are Client variables (Store in client-side) and Site properties which are consider like configuration file.
What If I want to use concept of Session in reactive web app to store sensitive data related to each user.
Outsystems reactive apps is like any frontend technology like Angular or Vue ..etc.
Your sensitive data must saved on your server like on the database and retrieve it by GetUserId(), also you can use forge component or extension (C# code) that allow you to store data in server memory (RAM) for rapid access.
Thanks @Ahmed Essawy for your declaration and contribution