Catechism of the Catholic Church §1921 — excerpt
Authority is exercised legitimately if it is committed to the common good of society. To attain this it must employ morally acceptable means.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.