HTTP 403

"[1]: §15.5.4 Error 401: "The 401 (Unauthorized) status code indicates that the request has not been applied because it lacks valid authentication credentials for the target resource.

"[1]: §15.5.2 The Apache web server returns 403 Forbidden in response to requests for URL[2] paths that corresponded to file system directories when directory listings have been disabled in the server and there is no Directory Index directive to specify an existing file to be returned to the browser.

Some administrators configure the Mod proxy extension to Apache to block such requests and this will also return 403 Forbidden.

Microsoft IIS responds in the same way when directory listings are denied in that server.

[2] A 403 status code can occur for the following reasons:[3] Client request:[4] Server response:[4]