code: public List<List<String>> getPermissionsForUserInDomain(String user, String domain) {
          return getFilteredPolicy(0, user, domain);
      }
docs: getPermissionsForUserInDomain gets permissions for a user or role inside a domain.
  
  @param user the user.
  @param domain the domain.
  @return the permissions, a permission is usually like (obj, act). It is actually the rule without the subject.