Utility function to validate apple identity token and return back apple userid using apple identity token and userid

ExternalAPIService.js

const APPLE_KEYS_URL = "https://appleid.apple.com/auth/keys";
const APPLE_ISS_URL = "https://appleid.apple.com";

const validateAppleIdentityToken = async (identityToken, appleUserId) => {
  const { data } = await axios.get(APPLE_KEYS_URL);
  const applePublicKey = data;
  const tokenDecodedHeader = jwtDecode(identityToken, { header: true });
  const kid = tokenDecodedHeader.kid;
  const sharedKid = applePublicKey.keys.filter((x) => x["kid"] === kid)[0]?.[
    "kid"
  ];

  const client = new JwksClient({
    jwksUri: APPLE_KEYS_URL,
  });
  const key = await client.getSigningKey(sharedKid);
  const signingKey = key.getPublicKey();
  try {
    const response = jwt.verify(identityToken, signingKey);
    if (response.iss !== APPLE_ISS_URL) {
      throw new Error("Invalid Apple Identity token");
    }
    return { appleId: appleUserId };
  } catch (e) {
   throw new Error("Invalid Apple Identity token");
  }
};