What is the mechanics of user login in a system?

The login mechanics include:

1. Data entry: The user enters identification data (e.g., login/email and password) into form fields.
2. Request submission: The data is sent to the server via HTTPS protocol.
3. Server validation: The server checks the correctness of the entered data (format, presence).
4. Authentication: The server searches for the user in the database based on the entered identifiers and compares the hash of the entered password with the hash stored in the database.
5. Authorization: If authentication is successful, the server determines the user's access rights to resources.
6. Response formation:
   • On successful login: The server generates a token (e.g., JWT, session ID) and sends it to the client (often in the response header or cookie). Additional user information may also be sent.
   • On failed login: The server sends an error response (e.g., "Invalid login or password").
7. Client response handling:
   • On successful login: The client saves the token (e.g., in Local Storage, Session Storage, cookie) and redirects the user to a protected page.
   • On failed login: The client displays an error message to the user.

Example of a request structure (simplified):

// POST /api/v1/login
{
  "username": "user@example.com",
  "password": "mysecretpassword"
}

Example of a successful response:

// 200 OK
{
  "token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...",
  "userId": 1,
  "role": "user"
}

Example of an error response:

// 401 Unauthorized
{
  "message": "Invalid credentials"
}