# File lib/aws/core/authorize_v4.rb, line 120
      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