Network Working Group R. Fielding Request for Comments: 2616 ...

Allow = "Allow" ":" #MethodExample of use:Allow: GET, HEAD, PUTThis field cannot prevent a client from trying other methods.However, the indications given by the Allow header field valueSHOULD be followed. The actual set of allowed methods is definedby the origin server at the time of each request.The Allow header field MAY be provided with a PUT request torecommend the methods to be supported by the new or modifiedresource. The server is not required to support these methods andSHOULD include an Allow header in the response giving the actualsupported methods.Fielding, et al. Standards Track [Page 106]RFC 2616 HTTP/1.1 June 1999A proxy MUST NOT modify the Allow header field even if it does notunderstand all the methods specified, since the user agent mighthave other means of communicating with the origin server.14.8 AuthorizationA user agent that wishes to authenticate itself with a server--usually, but not necessarily, after receiving a 401 response--doesso by including an Authorization request-header field with therequest. The Authorization field value consists of credentialscontaining the authentication information of the user agent forthe realm of the resource being requested.Authorization = "Authorization" ":" credentialsHTTP access authentication is described in "HTTP Authentication:Basic and Digest Access Authentication" [43]. If a request isauthenticated and a realm specified, the same credentials SHOULDbe valid for all other requests within this realm (assuming thatthe authentication scheme itself does not require otherwise, suchas credentials that vary according to a challenge value or usingsynchronized clocks).When a shared cache (see section 13.7) receives a request