adjustAutoExposure.swift

func exposeAtPoint(point: CGPoint) {
  let device = activeInput.device // var activeInput: AVCaptureDeviceInput!
  if device.isExposurePointOfInterestSupported && device.isExposureModeSupported(.continuousAutoExposure) {
    do {
      try device.lockForConfiguration()
      device.exposurePointOfInterest = point
      device.exposureMode = .continuousAutoExposure
      
      if device.isExposureModeSupported(.locked) {
        device.addObserver(self, forKeyPath: "adjustingExposure", options: .new, context: &adjustingExposureContext)
        device.unlockForConfiguration()
      }
    } catch {
      print("Error exposing on POI: \(error.localizedDescription)")
    }
  }
}