Thanks a lot to everybody for the replies.
Kurt: by the term "client" I meant an application, like psql, from which users could connect to the database, as they have a user/password, and manipulate data. I want them to access from certain, specific application, but I don't want them to install psql, for example, and have also access through it.
I liked Chris Carver idea of modifing user/password: quite simple and efective.
But thank you all people, you gave me some fine ideas.
Best regards,
Mario
