code: async function createPrivateKey(size = 2048) {
      let pemKey;
  
      /* Native implementation */
      if (nativeGenKeyPair) {
          const result = await nativeGenKeyPair('rsa', {
              modulusLength: size,
              publicKeyEncoding: { type: 'spki', format: 'pem' },
              privateKeyEncoding: { type: 'pkcs8', format: 'pem' }
          });
  
          pemKey = result[1];
      }
      /* Forge implementation */
      else {
          const keyPair = await forgeGenKeyPair({ bits: size });
          pemKey = forge.pki.privateKeyToPem(keyPair.privateKey);
      }
  
      return Buffer.from(pemKey);
  }
docs: Generate a private RSA key
  
  @param {number} [size] Size of the key, default: `2048`
  @returns {Promise<buffer>} Private RSA key