auth.ts

import {
  AppleAuthenticationScope,
  signInAsync,
} from "expo-apple-authentication";
import {
  CryptoDigestAlgorithm,
  digestStringAsync,
  randomUUID,
} from "expo-crypto";

/**
 * Initiates the auth flow for the native Apple Sign In.
 * Returns the token and nonce that will later be passed
 * to Supabase to complete the sign in.
 */
export async function initiateAppleSignIn() {
  const rawNonce = randomUUID();
  const hashedNonce = await digestStringAsync(
    CryptoDigestAlgorithm.SHA256,
    rawNonce,
  );

  const credential = await signInAsync({
    requestedScopes: [
      AppleAuthenticationScope.FULL_NAME,
      AppleAuthenticationScope.EMAIL,
    ],
    nonce: hashedNonce,
  });

  const token = credential.identityToken;
  if (!token) throw new Error("No id token");

  return { token, nonce: rawNonce };
}