Login With Apple

It'd be cool if we had Sign in with apple ([docs](https://developer.apple.com/sign-in-with-apple/get-started/)), which would allow for some cool auth schemes in drink apps.

Start with the linked Apple Sign in documentation and inspect the Flask endpoint described as linking external accounts into LDAP. Define the integration and acceptance criteria for authenticating with Apple and linking that account. Done means the requested Sign in with Apple flow is supported.

索引モデルが issue の本文から書いたものです。