// $leeway is needed for clock skew
Firebase\JWT\JWT::$leeway = 60;

$provider = new League\OAuth2\Client\Provider\Apple([
    'clientId'          => '{com.muse.appleoauth}',
    'teamId'            => '{RR25RMZPY3}', // 1A234BFK46 https://developer.apple.com/account/#/membership/ (Team ID)
    'keyFileId'         => '{2MHN8Z76CJ}', // 1ABC6523AA https://developer.apple.com/account/resources/authkeys/list (Key ID)
    'keyFilePath'       => '{AuthKey_2MHN8Z76CJ.p8}', // __DIR__ . '/AuthKey_1ABC6523AA.p8' -> Download key above
    'redirectUri'       => 'https://auth.museapp.art/appleoauth',
]);

if (!isset($_POST['code'])) {

    // If we don't have an authorization code then get one
    $authUrl = $provider->getAuthorizationUrl();
    $_SESSION['oauth2state'] = $provider->getState();
    header('Location: '.$authUrl);
    exit;

// Check given state against previously stored one to mitigate CSRF attack
} elseif (empty($_POST['state']) || ($_POST['state'] !== $_SESSION['oauth2state'])) {

    unset($_SESSION['oauth2state']);
    exit('Invalid state');

} else {

    // Try to get an access token (using the authorization code grant)
    /** @var AppleAccessToken $token */
    $token = $provider->getAccessToken('authorization_code', [
        'code' => $_POST['code']
    ]);

    // Optional: Now you have a token you can look up a users profile data
    // Important: The most details are only visible in the very first login!
    // In the second and third and ... ones you'll only get the identifier of the user!
    try {

        // We got an access token, let's now get the user's details
        $user = $provider->getResourceOwner($token);

        // Use these details to create a new profile
        printf('Hello %s!', $user->getFirstName());

    } catch (Exception $e) {

        // Failed to get user details
        exit(':-(');
    }

    // Use this to interact with an API on the users behalf
    echo $token->getToken();
}