Generate an access token for Sign in With Apple

genAppleToken.js

const jwt = require('jsonwebtoken');
const fs = require('fs');
const privateKey = fs.readFileSync('/Path/To/appleAuth/key.p8');
const client_id = 'YOUR_CLIENT_ID';
const team = 'YOUR_TEAM_ID';
const key_id = 'YOUR_KEY_ID';

function _generateToken(clientId, teamId, pk, exp, keyid) {
    try {
        const claims = {
            iss: teamId,
            iat: Math.floor(Date.now() / 1000),
            exp,
            aud: 'https://appleid.apple.com',
            sub: clientId
        };

        return jwt.sign(claims, pk, {
            algorithm: 'ES256',
            keyid
        });
    } catch (err) {
        throw new Error(
            'AppleAuth Error - Error occurred while signing: ' + err
        );
    }
}

function generateToken() {
    const sixMonthExpiry = Math.floor(Date.now() / 1000) + 86400 * 180;
    return _generateToken(
        client_id,
        team,
        privateKey,
        sixMonthExpiry,
        key_id
    );
}

console.log(generateToken()); // eslint-disable-line