How to add/remove role or claim to user at run time

in asp.net mvc we decorate authorized attrbute with role name when we code but think the situation is different that admin user want the ability to add/remove role or claim to user at run time. i search google for a nice article on this sibject but found none.

 

so anyone can guide me how to develop system as a result we can attach or remove role to user at run time. waiting for good help. thanks