Client Error 4xx *

The 4xx class of status code is intended for cases in which the client seems to have erred. These status codes are applicable to any request method.

400 Bad Request

The request could not be understood by the server due to malformed syntax. The client should not repeat the request without modifications. 1

401 Unauthorized

The request requires user authentication. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource. The client may repeat the request with a suitable Authorization header field . If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user should be presented the entity that was given in the response, since that entity may include relevant diagnostic information.

403 Forbidden

The server understood the request, but is refusing to fulfill it. Authorization will not help and the request should not be repeated. If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled, it should describe the reason for the refusal in the entity body. This status code is commonly used when the server does not wish to reveal exactly why the request has been refused, or when no other response is applicable.

404 Not Found

The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent. If the server does not wish to make this information available to the client, the status code 403 (forbidden) can be used instead.

407 Proxy Authentication Required **

This code is similar to 401 (Unauthorized), but indicates that the client MUST first authenticate itself with the proxy.

409 Conflict **

The request could not be completed due to a conflict with the current state of the resource. Ideally, the response entity would include enough information for the user or user agent to fix the problem; however, that may not be possible and is not required.

* Extracted from RFC 1945, "Hypertext Transfer Protocol -- HTTP/1.0", Berners-Lee, et.al., 1996
** Extracted from RFC 2068, "Hypertext Transfer Protocol -- HTTP/1.1", R. Fielding, et.al., 1997
1. The WASD HTTP server generally uses this status code to represent any request containing incorrect or missing information.