function generateAuthCode(secret) {
    secret = new Buffer(secret, 'base64');

    var time = Math.floor(Date.now() / 1000);

    var buffer = new Buffer(8);
    buffer.writeUInt32BE(0, 0); // This will stop working in 2038!
    buffer.writeUInt32BE(Math.floor(time / 30), 4);

    var hmac = require('crypto').createHmac('sha1', secret);
    hmac = hmac.update(buffer).digest();

    var start = hmac[19] & 0x0F;
    hmac = hmac.slice(start, start + 4);

    var fullcode = hmac.readUInt32BE(0) & 0x7fffffff;

    var chars = '23456789BCDFGHJKMNPQRTVWXY';

    var code = '';
    for(var i = 0; i < 5; i++) {
        code += chars.charAt(fullcode % chars.length);
        fullcode /= chars.length;
    }

    return code;
};

generateAuthCode('fWkXbmF1M6QfnGUzy+Z2RUb23JE=')