class Aws::Signers::S3

def canonicalized_headers(request)
  x_amz = request.headers.select{|k, v| k =~ /^x-amz-/i }
  x_amz = x_amz.collect{|k, v| [k.downcase, v] }
  x_amz = x_amz.sort_by{|k, v| k }
  x_amz = x_amz.collect{|k, v| "#{k}:#{v.to_s.strip}" }.join("\n")
  x_amz == '' ? nil : x_amz
end