My goal is to retrieve Google Voice voicemail audio messages and download them.
On May 27, 2015 - Google permanently disabled the ClientLogin API for Google Voice and encouraged migration to OAuth2.0.
I created a project in the Google Developers Console, but I was unable to identify the API that should be used. I am not alone (Google voice PHP OAuth 2.0).
It seems unlikely to me that Google would permanently disable the Google Voice ClientLogin API without having a working solution available - especially since they deprecated the GV ClientLogin API more than 2 years ago and left it available for use for so long afterwards.
After further research, I discovered that the GMail API permits downloading of attachments.
Theoretically, if I set Google Voice to forward all Voicemails to GMail, I could download the audio file using the GMail API (gmail.users.messages.attachments.get).
NOTE: I am not certain that this will work! I worry it may not because when you click on Play Message in Gmail, it forwards to the Google Voice page - where you can choose to download the message. It seems this approach may result in needing a Google Voice API as well.
How are we supposed to retrieve Google Voice voicemail audio messages and download them using OAuth2.0?