First step done,

    below  is  the patch to have views to override the permission
    checks for the accessed tables. Now we can do the following:

    CREATE VIEW db_user AS SELECT
         usename,
         usesysid,
         usecreatedb,
         usetrace,
         usecatupd,
         '**********'::text as passwd,
         valuntil
        FROM pg_user;

    REVOKE ALL ON pg_user FROM public;
    REVOKE ALL ON db_user FROM public;
    GRANT SELECT ON db_user TO public;