Check logon rights of user in Postgres

Question

How to check that some user has logon rights? I want to show current logon right and allow other user to enable to disable it.

Something like

IF pg_can_login('someuser')
  ALTER ROLE someuser NOLOGIN;
ELSE
  ALTER ROLE someuser LOGIN;
ENDIF

How to implement pg_can_login(user) in SQL or in plPgSQL?

Answer 1

This is accessible through pg_roles

select rolcanlogin
from pg_roles
where rolname = 'someuser';

Answer 2

Something like:

DO $$
BEGIN
  IF (select rolcanlogin from pg_roles where rolname = 'aklaver') THEN
     RAISE NOTICE 'yes';
  ELSE
     RAISE NOTICE 'no';
  END IF;
END;
$$
;

NOTICE:  yes
DO