Nhibernate foreign key to foreign key collection mapping?

<bag name="SecuredPages"  lazy="true" inverse="false" cascade="none">
      <key column="RoleId" />
      <many-to-many class="RealEstate.Core.Domain.SecuredPage,RealEstate.Core" />
</bag>

SecuredPage.RoleId = Staff.id

SecurePage.RoleId = Staff.StaffLevel