From Pathfinder Lost Omens Divine Mysteries, which isn't enabled.

Aura Expertise

FEAT 16

Activity free action

Prerequisites Battle Harbinger Dedication

Trigger Your turn begins.

You've become so accustomed to maintaining your battle auras that it's become second nature to you. You immediately gain the effects of the Sustain action for one of your battle auras.

Pathfinder Lost Omens Divine MysteriesORC