Sign in with Apple

See https://developer.okta.com/blog/2019/06/04/what-the-heck-is-sign-in-with-apple for the steps on the Apple side.

Provider configuration:

{
  "issuer": "https://appleid.apple.com",
  "jwks_uri": "https://appleid.apple.com/auth/keys",
  "authorization_endpoint": "https://appleid.apple.com/auth/authorize",
  "token_endpoint": "https://appleid.apple.com/auth/token"
}

Client configuration:

{
  "client_id": "<services-id>",
  "client_secret": "eyJraWQiOiIzUjhIVTJTOFJLIiwiYWxnIjoiRVMyNTYifQ.<etc>"
}

Custom configuration:

{
  "scope": "openid email name",
  "token_endpoint_auth" : "client_secret_post"
}