code: public boolean addPermissionForUser(String user, List<String> permission) {
          return addPermissionForUser(user, permission.toArray(new String[0]));
      }
docs: addPermissionForUser adds a permission for a user or role.
  Returns false if the user or role already has the permission (aka not affected).
  
  @param user the user.
  @param permission the permission, usually be (obj, act). It is actually the rule without the subject.
  @return succeeds or not.