Implement a web service that provides a sitemap

Question

Hi, I have a complex web site in ASP.NET and c# using a class that inherits from XmlSiteMapProvider to build a site map used by asp:menu through asp:SiteMapDataSource. I would like to build a web service that given the user details will provide the map (based on user roles).

1)I already have the class that inherits from XmlSiteMapProvider that is used at the moment in my website, how can I explicitly generate a site map? (taking into account all the web.config files I have in my web site's directory)

2)What should I generate? a XmlSiteMapProvider object?

3)How do I use the object generated by the web service (or whatever my web service will return) using asp:menu?