Restrict access to parts of sitemap

[321los]

Hi,

right now, I am creating a Lucene index with this entry in my sitemap:

<map:match pattern="buildIndex">
        <map:generate src="" href="http://localhost:8080//index.xml">http://localhost:8080//index.xml "/>
       <map:transform type="index"/>
       <map:serialize type="xml"/>
 </map:match>

<map:match pattern="index.xml">
              <map:generate type="file" src=""
              <map:transform type="sql">
                  <map:parameter name="use-connection" value="mysql-pool"/>
             </map:transform>
             <map:transform src=""
             <map:serialize type="xml"/>
 </map:match>

which means every (outside) user could be able to start the index when calling buildIndex. I would like to avoid that. Question is: how?
Internal pipeline would help for index.xml, but for buildIndex?

Thanks for your answers
Marco