Get public key from certificate in nodejs - node.js

Question

I need to get a server's public key from its SSL cert. I'm getting the cert as follows:
https.request(options, res => {
const cert = res.connection.getPeerCertificate();
const publicKey = cert.????()
}
I can't find a way to get the public key from the certificate though. Are there any libraries that can do this?
I'm looking to use the public key to encrypt some data:
const encryptedBuffer = crypto.publicEncrypt({
key: publicKey,
padding: crypto.constants.RSA_PKCS1_PADDING
}, utf8Payload)
I see that the certificate has a "raw" buffer, but using that as the publicKey fails.

Answer 1

-----BEGIN CERTIFICATE-----
MIID3DCCAsSgAwIBAgIUOaZ5jqRgBz4HjwilIbDz5+Polh0wDQYJKoZIhvcNAQEL
BQAwXjELMAkGA1UEBhMCQ04xEzARBgNVBAoTClRlbnBheS5jb20xHTAbBgNVBAsT
.....
C1c3RqArBaz/c4SqHhyKaHRFinDs5kjnAz+H4+QvQAH0UXgHG050YEZjeZPXMRJB
4I0fzGC++82WXhcwSPaX+BJZuv2bEIfxbyxdVanGmIJdYsGFwSc9sIf2j1cK22A5
vdboEXXkQnqF552iNy9HGRubNQ1VkqITELToRcqcvAo=
-----END CERTIFICATE-----
If the format of the certificate is as above, it can be done with crypto module. No dependency on other packages.
crypto.createPublicKey(cert).export({type:'spki', format:'pem'})
output format:
-----BEGIN PUBLIC KEY-----
..........................
-----END PUBLIC KEY-----
or
crypto.createPublicKey(cert).export({type:'pkcs1', format:'pem'})
output format:
-----BEGIN RSA PUBLIC KEY-----
..............................
-----END RSA PUBLIC KEY-----
see more on the document

Answer 2

I see that the certificate has a "raw" buffer, but using that as the
publicKey fails.
Note that the raw buffer is DER encoded, and from crypto.publicEncrypt needs a PEM encoded key. So, you just need to do the conversion. I've used node-openssl-wrapper in the example below, but there are other libraries that also convert DER to PEM,
const ossl = require('openssl-wrapper')
const https = require("https");
https.request(options, res => {
const certificate = res.connection.getPeerCertificate();
const rawDer = certificate.raw;
ossl.exec('x509', rawDer, { inform: 'der', outform: 'pem' }, (err, buffer) => {
const publicKey = buffer.toString('utf8'); // PEM encoded public key safe to use now
// crypto.publicEncrypt({ key: publicKey, ...
})
});