Re:

"lise chhay" <lise(dot)chhay(at)mail(dot)com> writes:
> J have created the user auth under Unix and I did :
> # su - postgres
> postgres$ createuser auth
> User auth created
> postgres$ psql auth
> auth=# INSERT INTO groupes (groupe, descr) VALUES ('auth', 'Administrateurs de la base Auth') ;
> auth=# INSERT INTO utilisateurs (login, password, nom, prenom) VALUES ('auth', 'tnnxiPQeNdFYs', 'auth', 'auth') ;
> auth=# INSERT INTO membres (login, groupe) VALUES ('auth', 'auth') ;

You have not set a Postgres password for this user. (I don't know what
"utilisateurs" is, but it's definitely not what Postgres will consult.)
Use the ALTER USER command to set the correct password.

regards, tom lane