presto-hive/src/main/java/io/prestosql/plugin/hive/security/SqlStandardAccessControlMetadata.java/SqlStandardAccessControlMetadata/listRoles
class SqlStandardAccessControlMetadata:    @Override
    public Set<String> listRoles(ConnectorSession session)
    {
        return ImmutableSet.copyOf(metastore.listRoles());
    }