The HTTP verb (GET, PUT, HEAD, DELETE) the request to sign
TODO: We need to know the HTTP verb in order to
create the authentication signature, but we don't
have easy access to it through the request object.
Maybe it'd be better for the S3 signer (or all signers?)
to work directly off of the HttpRequest instead of
the Request object?
The canonical resource path portion of the S3 string to sign.
Examples: "/", "/<bucket name>/", or "/<bucket name>/<key>"
TODO: We don't want to hold the resource path as member data in the S3
signer, but we need access to it and can't get it through the
if (resourcePath == null)