    # File lib/fog/aws.rb, line 90
        def self.signed_params(params, options = {})
          params.merge!({
            'AWSAccessKeyId'    => options[:aws_access_key_id],
            'SignatureMethod'   => 'HmacSHA256',
            'SignatureVersion'  => '2',
            'Timestamp'         => Time.now.utc.strftime("%Y-%m-%dT%H:%M:%SZ"),
            'Version'           => options[:version]
          })

          params.merge!({
            'SecurityToken'     => options[:aws_session_token]
          }) if options[:aws_session_token]

          body = ''
          for key in params.keys.sort
            unless (value = params[key]).nil?
              body << "#{key}=#{escape(value.to_s)}&"
            end
          end
          string_to_sign = "POST\n#{options[:host]}:#{options[:port]}\n#{options[:path]}\n" << body.chop
          signed_string = options[:hmac].sign(string_to_sign)
          body << "Signature=#{escape(Base64.encode64(signed_string).chomp!)}"

          body
        end