# File lib/aws/core/signature/version_4.rb, line 97
        def canonical_headers
          headers = []
          self.headers.each_pair do |k,v|
            headers << [k,v] unless k == 'authorization'
          end
          headers = headers.sort_by(&:first)
          headers.map{|k,v| "#{k}:#{canonical_header_values(v)}" }.join("\n")
        end