I love this question and it reminds me that I have been slacking utterly in my political reading (and I have been into other things), but to me as a "statist" authority (all authority, the authority of a father over his household, the Pope over other humans, and governments over their subjects, and particular instances in other situations) ultimately comes from God. One thing I do not hold and absolutely reject is that it comes from consent, the question of consent is as irrelevant to the subject of authority as nooch is irrelevant to the subject of astrophysics.
Concerning the government though, how this authority appears in the world and how it is taken away (although I hold that even tyrannical action in part does not take it away as a whole but only in that instance) is interesting and there are many opinions on that which I need to study more.
But, in my opinion, that it comes from God ultimately is clear, for the Scripture says "
the power of the earth is in the hand of the Lord, and in due time he will set over it one that is profitable," and the Lord said "
you would have no authority over Me if it were not given to you from above," and St. Paul says speaking of God's hierarchy "
let every person be subject to the governing authorities, for there is no authority except by God, and those that exist are put in place by God."
Due to this I have a very fatherly conception of the state and will often say "a good state is like a good father."
All of that is just my opinion of course.