Filtering Portal Role by their Permission

We are writing a WebDynpro application that needs to search for roles that have specific permission assigned to them. For example, we need to display all protal roles for which Content Administrators have 'Role Assigner' privilege to.

Does anyone know which API's to use. The com.sap.security.api does not seem to have any methods related to role permissions. Sample code would be great.

Maximum points to the first helpful answer.