Error - Insufficient credentials while making the connection for push notification - ios

Question

I am trying to deliver push notification in my ios app and i user node.js. So I am followint the tutorial from the link: https://blog.engineyard.com/2013/developing-ios-push-notifications-nodejs.
In this tutorial they are keeping the passphrase for the private key as empty. But I am setting a password for my private key and I dont know how to include my password in the coding. I know there has been many angles of answer to this. But am not getting anything works. I tried :
.set('cert file', join(__dirname, '../_cert/apn-dev-cert.pem'))
.set('key file', join(__dirname, '../_cert/apn-dev-key.pem'))
//or this works too:
// .set('pfx file', join(__dirname, '../_cert/Certificates.p12'))
// .set('passphrase', 'your passphrase')
.enable('sandbox')
agent.on('message:error', function (err, msg) {
connect.log('error1');
switch (err.name) {
// This error occurs when Apple reports an issue parsing the message.
case 'GatewayNotificationError':
console.log('[message:error] GatewayNotificationError: %s', err.message);
// The err.code is the number that Apple reports.
// Example: 8 means the token supplied is invalid or not subscribed
// to notifications for your application.
if (err.code === 8) {
console.log(' > %s', msg.device().toString());
// In production you should flag this token as invalid and not
// send any futher messages to it until you confirm validity
}
break;
// This happens when apnagent has a problem encoding the message for transfer
case 'SerializationError':
console.log('[message:error] SerializationError: %s', err.message);
break;
// unlikely, but could occur if trying to send over a dead socket
default:
console.log('[message:error] other error: %s', err.message);
break;
}
});
/*!
* Make the connection
*/
agent.connect(function (err) {
// gracefully handle auth problems
if (err && err.name === 'GatewayAuthorizationError') {
console.log('Authentication Error: %s', err.message);
process.exit(1);
}
// handle any other err (not likely)
else if (err) {
console.log('error1');
throw err;
}
// it worked!
var env = agent.enabled('sandbox')
? 'sandbox'
: 'production';
console.log('apnagent [%s] gateway connected', env);
});
I also tried concatenating the certificate and the key and use it as a single file, nothing works.