How does the server identify the user with the session id?

Question

Sessions

I don't quite understand how this happens. For example:

1. The user visits the site - sends a request. The server sends a response along with a unique session_id.
   
2. The user passes authorization - enters login and the password.
   
3. The user is logged into their account. There it sends different requests to the server.
   

How does the server understand that all requests are from the same client? Relatively speaking, the server writes to itself in some kind of temporary storage (it is valid only for the duration of the session) that such and such a session_id is such and such a user_id? Is the ip address used to identify the user?

Answer 1

The user has a session identifier entered in the cookie (actually, the file name if the sessions are stored in files or the key name if the sessions are stored, for example, in Redis or some other in-memory database).
Whether to use IP for additional identification or some other property of the client is up to the application developer.
When a user sends a request to the server, there is also a cookie with the session ID in the request headers, so the server will know who sent the request.