In what cases can an Unauthorized error occur?

Unauthorized (401) error occurs when a request to the server requires authentication, but it was not provided or is incorrect (for example, wrong login/password, expired token).

Common reasons:

• Missing credentials (no Authorization header).
• Incorrect format of the Authorization header.
• Invalid credentials (wrong login/password).
• Expired or invalid authentication token (e.g., JWT, OAuth token).
• Attempting to access a resource that requires authentication without logging in first.
• Authentication process failure on the server side.