Ah, OK. In that case you need someone to answer who actually knows how the camera works and how the Authenticator app works.
Or you could try to automate the clunky process. I think at one stage I was using the Camera postprocess script to look for new images and see whether they are QR codes, so that the mere act of photographing a QR code results in the processing of the QR code (subject to personal security requirements). See also: QR code scanning via megapixels
Edit: Or eventually the Camera app may recognise QR codes automatically and then “all” you need to do is hook in the right processing for an otpauth: QR code if indeed the Camera app doesn’t do the right thing automatically.