That is a tautology. Who provides the justification and who gave them that authority. The king? The nobles? The learned? The majority? The masses? The individual?
The problem with power is it is self justifying. If you have power you can justify anything, and if you do not, you exist at the mercy of those that do. One would think the most rational behavior would be to give those power that want it least (such as anarchists), but human psychology shows that significant portions of humanity want hierarchies and will gladly give their power to put a dictator/king into power.