def url_for(method, options = {})
req = request_for_signing(options)
method = http_method(method)
expires = expiration_timestamp(options[:expires])
req.add_param("AWSAccessKeyId", config.signer.access_key_id)
req.add_param("versionId", options[:version_id]) if options[:version_id]
req.add_param("Signature", signature(method, expires, req))
req.add_param("Expires", expires)
req.add_param("x-amz-security-token", config.signer.session_token) if
config.signer.session_token
build_uri(options[:secure] != false, req)
end