An OPTIONS request with an asterisk ("*") as the request-target
(Section 5.3 of [RFC7230]) applies to the server in general rather
than to a specific resource. Since a server's communication options
typically depend on the resource, the "*" request is only useful as a
"ping" or "no-op" type of method; it does nothing beyond allowing the
client to test the capabilities of the server. For example, this can
be used to test a proxy for HTTP/1.1 conformance (or lack thereof).
If the request-target is not an asterisk, the OPTIONS request applies
to the options that are available when communicating with the target
resource.
http://tools.ietf.org/html/rfc7231#section-4.3.7