Catholics: Pope Nicholas V authorized perpetual slavery in "Dum Diversas". What scripture did he rely upon?

From Wikipedia: "Dum Diversas is a papal bull issued on 18 June 1452 by Pope Nicholas V. It authorised Alfonso V of Portugal to reduce any "Saracens (Muslims) and pagans and any other unbelievers" to perpetual slavery. This facilitated the Portuguese slave trade from West Africa." Do you know... show more From Wikipedia: "Dum Diversas is a papal bull issued on 18 June 1452 by Pope Nicholas V. It authorised Alfonso V of Portugal to reduce any "Saracens (Muslims) and pagans and any other unbelievers" to perpetual slavery. This facilitated the Portuguese slave trade from West Africa."

Do you know what scripture he used to make this decision?
When was this papal bull reversed, by whom, and by what scriptural authority?
Has a pope ever apologized on behalf of the Church for authorizing slavery, as John Paul II apologized to the Jews for Catholic persecution?

Why is this not a contradiction of papal infallibility?

(and lest anyone think I'm out to bash Catolics, there were many churches that sanctioned slavery, such as the Southern Baptists who broke away from the Baptists specifically to recognize the scriptural basis for slavery...I'll get to you presently).
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