I would use "Sign In with Apple" in the web via Apple JS. The code example can be found here: https://developer.apple.com/documentation/signinwithapplejs/configuring_your_webpage_for_sign_in_with_apple
The question now is: what is the Client ID and where can I find it. I tested the identifier of the app id on https://developer.apple.com/account/resources/identifiers/list and I tested the identifier of the service id. If I click on the button and verify with Touch ID on my mac, I got the error "AUTH_ALERT_SIGN_UP_NOT_COMPLETED":
This is the used code:
<html>
<head>
</head>
<body>
<button id="sign-in-with-apple-button"> Sign In with Apple </button>
<script type="text/javascript" src="https://appleid.cdn-apple.com/appleauth/static/jsapi/appleid/1/en_US/appleid.auth.js"></script>
<script type="text/javascript">
AppleID.auth.init({
clientId : 'unknown',
scope : 'email',
redirectURI: 'https://mytld/test.php',
state : 'DE'
});
const buttonElement = document.getElementById('sign-in-with-apple-button');
buttonElement.addEventListener('click', () => {
AppleID.auth.signIn();
});
</script>
</body>
</html>
I got no request on test.php.
Client ID is the "Identifier" of your Service ID that has "Sign In with Apple" enabled:
Apple recommends you make it the following format on the Register a Service ID screen: