The latest HA Podcast mentioned that you can just do OAuth with Alexa now. I haven’t seen any documentation on how to do that yet, though. Playing around this morning, I’ve been able to use the account linking to HA with a custom skill, but haven’t pushed it past that yet.
In the Amazon Developer Console, under your skill, Build, and then account linking, you can set up the OAuth flow.
This at least seems to auth, but I need to create/set up my intents again for reasons unrelated to this change. The client ID seems to require coming from the same location that the amazon-generated redirect url will be, which is why I had to use pitangui - but there are three listed redirect URLS on the bottom of that page, so I’m not sure what the truly correct thing to here yet.