Systems Design Concepts Practice Test

Authentication required in HTTP is signaled by the 401 Unauthorized status. This means the request lacks valid authentication credentials for the target resource, or they were not provided at all. The server uses 401 to prompt the client to authenticate, often with a WWW-Authenticate header describing the required method. Once the client supplies valid credentials, the server may respond with a success code or another appropriate status depending on the outcome. In contrast, 200 OK means the request succeeded and the response contains the requested data. 201 Created indicates a new resource was successfully created as a result of the request. 400 Bad Request means the server could not understand the request due to malformed syntax or invalid parameters, not an authentication issue.