The OPTIONS method represents a request for information about the communication options available on the request/response chain identified by the Request-URI. This method allows the client to determine the options and/or requirements associated with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
Unless the server's response is an error, the response MUST NOT include entity information other than what can be considered as communication options (e.g., Allow is appropriate, but Content-Type is not). Responses to this method are not cachable.
If the Request-URI is an asterisk ("*"), the OPTIONS request is intended to apply to the server as a whole. A 200 response SHOULD include any header fields which indicate optional features implemented by the server (e.g., Public), including any extensions not defined by this specification, in addition to any applicable general or response-header fields. As described in section 5.1.2, an "OPTIONS *" request can be applied through a proxy by specifying the destination server in the Request-URI without any path information.
If the Request-URI is not an asterisk, the OPTIONS request applies only to the options that are available when communicating with that resource. A 200 response SHOULD include any header fields which indicate optional features implemented by the server and applicable to that resource (e.g., Allow), including any extensions not defined by this specification, in addition to any applicable general or response-header fields. If the OPTIONS request passes through a proxy, the proxy MUST edit the response to exclude those options which apply to a proxy's capabilities and which are known to be unavailable through that proxy.