PHP’s openssl_sign Equivalent in Node JS

I am (slowly) learning Node JS and trying to use it in place of a PHP script I have. I need to sign a string I have assembled with SSL to pass on to a curl request.

In PHP, this is how I’ve done it:

$sig = '2018-08-24T17:33:41Z:abcdef:/path/to/api';

$pkeyid = openssl_pkey_get_private("file://YourMomGoesToCollege.pem"); 

// Sign 'sig' with private key
if(openssl_sign($sig, $signed_signature, $pkeyid, "sha256WithRSAEncryption")) {

  openssl_free_key($pkeyid);

  //Set curl header options ...
  curl_setopt($ch, CURLOPT_HTTPHEADER,
    [
    "X-Apple-CloudKit-Request-SignatureV1: " . base64_encode($signed_signature),
  ]
);

}

So I’m trying to generate the evuivalent of $signed_signature, but I’m not sure how to proceed. It seems like Node’s Crypto can do something similar, but its parameters seem different. This is my best guess:

const crypto = require('crypto')
const sign = crypto.createSign('SHA256')

sign.write(sig)
sign.end()

const privateKey = __dirname + 'YourMomGoesToCollege.pem'
var signedSignature = sign.sign(privateKey, 'hex')

var readyForCurl = Buffer.from(signedSignature).toString('base64')

Am I on the right track?

Answer

Using your work as a starting point and doing some minor modifications, the following snippets result in the same signature being printed (base64-encoded):

PHP:

$data = 'some data to sign';
$key = openssl_pkey_get_private('file://private.pem'); 

if(openssl_sign($data, $signature, $key, 'sha256WithRSAEncryption')) {
  openssl_free_key($key);
  $signature_b64 = base64_encode($signature);
  echo($signature_b64."n");
}

Node JS:

const crypto = require('crypto');
const sign = crypto.createSign('SHA256');
const fs = require('fs')

sign.write('some data to sign');
sign.end();

const key = fs.readFileSync('private.pem');
signature_b64 = sign.sign(key, 'base64');
console.log(signature_b64);

diff-ing the two:

$ diff <(php sign.php) <(node sign.js)

shows the outputs are the same.

I used this resource: iotdb-crypto-example