Explain the request processing sequence in a system.

The request processing in a system usually involves several stages:

1. Receiving the request — the server or application receives an incoming request from a client (e.g., an HTTP request).
2. Authentication and authorization — it checks whether the user has the rights to perform the requested action.
3. Parsing and validation — the request is parsed, and parameters are checked for correctness.
4. Business logic processing — necessary operations are performed, such as database queries or calculations.
5. Response formation — a response is created to be sent back to the client.
6. Sending the response — the response is transmitted back to the client.

In C#, this might look like the following in an ASP.NET web application:

public IActionResult HandleRequest(RequestModel request)
{
    if (!User.Identity.IsAuthenticated)
        return Unauthorized();

    if (!ModelState.IsValid)
        return BadRequest(ModelState);

    var result = _service.Process(request);
    return Ok(result);
}

Each stage is important for the correct and secure operation of the system.