code: def add_role_to_user(self, user, role):
          
          user, role = self._prepare_role_modify_args(user, role)
          if role not in user.roles:
              user.roles.append(role)
              self.put(user)
              return True
          return False
docs: Adds a role to a user.
  
          :param user: The user to manipulate
          :param role: The role to add to the user