If you go with GitHub - pow-auth/pow: Robust, modular, and extendable user authentication system · GitHub you get apple sign in out off the box with GitHub - pow-auth/assent: Multi-provider framework in Elixir · GitHub

You should call the callback method passing along the auth code:

config
|> Assent.Config.put(:session_params, %{})
|> Assent.Strategy.Apple.callback(%{"code" => apple_auth})
|> case do
  {:ok, %{user: _user, token: _token}} ->
    conn |> put_status(:ok) |> put_view(MyAppWeb.ErrorView) |> render(:"200")
  _ ->
    conn |> put_status(400) |> put_view(MyAppWeb.ErrorView) |> render(:"400") 
end

:session_params are required in Assent, but in this case it can just be an empty map as you don’t need to validate state.

Remember that the :redirect_uri in the config should match your app. If I remember correctly with Apple it just has to be nil or empty string, since there’s no redirect uri in the app:

config = [
  client_id: "REPLACE_WITH_SERVICES_ID",
  team_id: "REPLACE_WITH_TEAM_ID",
  private_key_id: "REPLACE_WITH_PRIVATE_KEY_ID",
  private_key_path: "/path/to/key.p8",
  redirect_uri: nil
]

Sorry, I should have had more information. Apple says they implemented the OpenID Connect standard, but from an article by Auth0 they say

Apple is using parts of the OAuth 2.0 and OpenID Connect (OIDC) standards.

So I guess another question would be does Ueberauth support OpenID connect flows? Or just the Oauth2 protocol.

I haven’t done much experimenting with the Apple Sign in API, and this question may have been a bit premature. Apologies for that.

EDIT: Apple sign in docs i’m looking at Sign in with Apple REST API | Apple Developer Documentation