const crypto = require('crypto');
const getCertIdentifier = (cert, unique = true) => {
try {
const x509 = new crypto.X509Certificate(Buffer.from(cert));
return unique ? x509.fingerprint256 : x509.serialNumber;
} catch {
return null;
}
};
const identifier = getCertIdentifier('<cert in pem format>');
Source: uNetworking/uWebSockets#1548 (comment)