Under ordained authority as a presbyter flowing from Christ, to the apostles, to the presbyters and to others, to whom (conditional) obedience is enjoined as those "over you" in the Lord. (Heb. 13:17) Whom is over you in the Lord that you are to obey? Under what authority did the Scribes and Pharisees sit in authority in the seat of Moses? Just make your argument, which has been already refuted.
Employing Hebrews 13:17 is not sufficient or useful in this case, because it was not the men qualified to be elders in the already-existing assemblies on Crete (no one knows how they were originally planted). Men not qualified to be elders in the Methodist Church can be elders in the Presbyterian Churches, so using a broad-brush excuse will not work here and now nor there and then.
It's pretty obvious that Titus' authority did not come from a board of elders, nor from a home church. Stick to the answer, a specific one. If you would, it shouldn't take a long time. So:
Under what authority did Titus conduct himself in Crete?