def sign(client, verb, path, headers={})
req_verb = verb.to_s.upcase
req_content_md5 = headers['Content-MD5']
req_content_type = headers['Content-Type']
req_date = headers['Date']
req_canonical_resource = "/#{client.bucket}/#{path}".split('?').first
req_canonical_amz_headers = ''
headers.keys.sort.select {|k| k =~ /^x-amz-/ }.each do |amz_key|
req_canonical_amz_headers << amz_key+':'+headers[amz_key]+"\n"
end
canonical_string_to_sign = "#{req_verb}\n"+
"#{req_content_md5}\n"+
"#{req_content_type}\n"+
"#{req_date}\n"+
"#{req_canonical_amz_headers}"+
"#{req_canonical_resource}"
digest = OpenSSL::Digest::Digest.new('sha1')
[OpenSSL::HMAC.digest(digest, client.connection.secret_access_key, canonical_string_to_sign)].pack("m").strip
end