Welcome to the first step in building our C#-based backend system. In this unit, we will focus on how to manage user data with expiration. This is a fundamental part of our project that will set the stage for more advanced features in later units.

Let's explore how to manage user data with expiration in a C# environment. We will cover the basic operations for managing user data:

1. Adding user data with an expiration time: This will ensure that user data is stored for a limited period and automatically deleted afterward.
2. Retrieving user data: This operation will help us fetch the user data we previously stored.

For demonstration purposes, we will use a simple in-memory storage mechanism along with System.Threading timers to simulate expiration functionality.

Here's a quick example of how we can structure these operations in C#: