This article lists standard and notable non-standard HTTP status codes. Standardized codes are defined by IETF as documented in Request for Comments (RFC) publications and maintained by the IANA. [1] Other, non-standard values are used by various servers. The descriptive text after the numeric code – the reason phrase – is shown here with typical value, but in practice, can be different or omitted. The HTTP 401 Unauthorized client error response status code indicates that a request was not successful because it lacks valid authentication credentials for the requested resource. The HTTP 401 status code, known as "401 Unauthorized," is a critical component in web security and user access control. It indicates that a request lacks valid authentication credentials and prevents unauthorized access to protected resources. HTTP specification defines these standard status codes divided into five categories that can be used to convey the results of a client’s request.
