# File lib/fog/aws/storage.rb, line 305
        def signature(params)
          string_to_sign =
"\#{params[:method].to_s.upcase}\n\#{params[:headers]['Content-MD5']}\n\#{params[:headers]['Content-Type']}\n\#{params[:headers]['Date']}\n"

          amz_headers, canonical_amz_headers = {}, ''
          for key, value in params[:headers]
            if key[0..5] == 'x-amz-'
              amz_headers[key] = value
            end
          end
          amz_headers = amz_headers.sort {|x, y| x[0] <=> y[0]}
          for key, value in amz_headers
            canonical_amz_headers << "#{key}:#{value}\n"
          end
          string_to_sign << canonical_amz_headers

          subdomain = params[:host].split(".#{@host}").first
          unless subdomain =~ /^(?:[a-z]|\d(?!\d{0,2}(?:\.\d{1,3}){3}$))(?:[a-z0-9]|\.(?![\.\-])|\-(?![\.])){1,61}[a-z0-9]$/
            Fog::Logger.warning("fog: the specified s3 bucket name(#{subdomain}) is not a valid dns name, which will negatively impact performance.  For details see: http://docs.amazonwebservices.com/AmazonS3/latest/dev/BucketRestrictions.html")
            params[:host] = params[:host].split("#{subdomain}.")[-1]
            if params[:path]
              params[:path] = "#{subdomain}/#{params[:path]}"
            else
              params[:path] = subdomain
            end
            subdomain = nil
          end

          canonical_resource  = @path.dup
          unless subdomain.nil? || subdomain == @host
            canonical_resource << "#{Fog::AWS.escape(subdomain).downcase}/"
          end
          canonical_resource << params[:path].to_s
          canonical_resource << '?'
          for key in (params[:query] || {}).keys.sort
            if %w{
              acl
              cors
              delete
              lifecycle
              location
              logging
              notification
              partNumber
              policy
              requestPayment
              response-cache-control
              response-content-disposition
              response-content-encoding
              response-content-language
              response-content-type
              response-expires
              torrent
              uploadId
              uploads
              versionId
              versioning
              versions
              website
            }.include?(key)
              canonical_resource << "#{key}#{"=#{params[:query][key]}" unless params[:query][key].nil?}&"
            end
          end
          canonical_resource.chop!
          string_to_sign << canonical_resource

          signed_string = @hmac.sign(string_to_sign)
          Base64.encode64(signed_string).chomp!
        end