How does XmlSiteMapProvider check user to be in specified role?

I roll my own SiteMapProvider inheriting System.Web.XmlSiteMapProvider.

I want to override logic of checking user to be in a role specified in siteMapNode's property roles:

<siteMapNode url="Add.aspx?type=user" title="Add user" roles="admin" />

How can I do that? Which class's member does XmlSiteMapProvider call to check that if securityTrimmingEnabled="true"?

abatishchev is close but does not provide a clear guidance. Calling base will apply the default asp.net access control rules. If you have custom rules, simply make your decision and return a bool.

public override bool IsAccessibleToUser(HttpContext context, SiteMapNode node)
{
     // use the properties of the context and node to determine accessibility.

     // only call base if you do not want to apply your custom rules
     // return base.IsAccessibleToUser(context, node);
}