    # File lib/fog/aws/signaturev4.rb, line 64
          def derived_hmac(date)
            kDate = @hmac.sign(date.utc.strftime('%Y%m%d'))
            kRegion = Fog::HMAC.new('sha256', kDate).sign(@region)
            kService = Fog::HMAC.new('sha256', kRegion).sign(@service)
            kSigning = Fog::HMAC.new('sha256', kService).sign('aws4_request')
            Fog::HMAC.new('sha256', kSigning)
          end