presto-main/src/main/java/io/prestosql/metadata/MetadataManager.java/MetadataManager/grantRoles
class MetadataManager:    @Override
    public void grantRoles(Session session, Set<String> roles, Set<PrestoPrincipal> grantees, boolean withAdminOption, Optional<PrestoPrincipal> grantor, String catalog)
    {
        CatalogMetadata catalogMetadata = getCatalogMetadataForWrite(session, catalog);
        CatalogName catalogName = catalogMetadata.getCatalogName();
        ConnectorMetadata metadata = catalogMetadata.getMetadata();

        metadata.grantRoles(session.toConnectorSession(catalogName), roles, grantees, withAdminOption, grantor);
    }