How to show different roles given to different users in Use case diagram?
<p>Let's say I have different functionalities/roles the admin can give to the users of their choice, so there is no "if the user can do this they can't do that". 
Example : I have the roles : read, add , delete and edit. The admin can assign these roles to his/her users, let's say randomly (for the lack of a better word).
Can this be illustrated in use case diagram or I should just use one actor and give him all these actions ? If it can be done then how ? And I am not familiar with all UML diagrams but I would be thankful if someone knows a better diagram where this can be illustrated better!</p>