Creating a thread-safe REST service for managing user posts

Develop a REST API that implements the following features:

1. An endpoint for saving a new message from a user.
2. An endpoint for retrieving a news feed: returns either all messages or only messages from a specific author based on the user_name parameter.

Implementation requirements:

• Data should be stored in memory (InMemory).
• The solution must be thread-safe.
• Follow object-oriented principles in the design.

Structure of the incoming request:

• Request:
  • user_name — a unique identifier of the author.
  • message — the message text.