I was reading a russian philosopher the other day, I forget his name now. He made the point that free will is the ultimate authority, that God Himself does not oppose our free will, even to the point of allowing us to willingly take ourselves to hell.
Authority in the Church is simply the reality that we experience within it. God speaks through our conscience, we respond by choosing to follow or ignore. We have the temporal authority because we can change, God has the eternal authority because He is not subject to change. We can choose to not become like God, that is human authority misused, or we can allow God to re-create His image in us through our repentance and thanksgiving, by giving and recieving mercy, we accept Gods authority to forgive us, he accepts our authority to forgive, in this way we offer back to Him something that was always His, and confess that he is the source of all things, including our own free decisions. Our decision to follow Him and Glorify Him unites us to Him. We then have the authority that Jesus had, to turn the other cheek, to forgive our enemies etc. without the grace of God, no-one has the authority to do these things, he is bound to his passions and always falls back into sin against his fellow creatures.
Looking for a single authority is a false and vain attempt to gain a totally objective viewpoint, a viewpoint only God can have. People who find such a viewpoint, as far as they are able, are saints and are aware of nothing but God, as long as they are aware of Him.