Latch - an Elixir atproto OAuth library

As part of building a service for automatically publishing blog posts from RSS feeds into atproto's standard.site lexicon, I implemented atproto OAuth for logging in and getting access tokens to publish for the user. This means that any user with an atproto account, whether they created it on Bluesky, Eurosky, or Blacksky, or any of the other Personal Data Servers available, can log in to your service. Atproto OAuth does not require pre-registering clients with a service, one implementation works across the entire ecosystem. The OAuth implementation is based on the 2.1 specification with some still in-draft extensions, and comes with some quirks compared to what you'd expect from older generations of OAuth. For example, access tokens can't be used as is, they need to come with a DPoP (demonstrating proof of possession) header signed for the specific request you're making, limiting what the access token can be used for if stolen. Additionally it includes PAR (push authorization…