module AWS::Core::Signature::Version4

def canonical_headers
  headers = []
  self.headers.each_pair do |k,v|
    header = [k.to_s.downcase, v]
    headers << header unless header.first == 'authorization'
  end
  headers = headers.sort_by(&:first)
  headers.map{|k,v| "#{k}:#{canonical_header_values(v)}" }.join("\n")
end