@panva/asn1.js/lib/asn1/encoders/pem.js

ASN.1 encoder and decoder for Node.js with no dependencies (fork of asn1.js using native BigInt)

const { inherits } = require('util')

const DEREncoder = require('./der')

function PEMEncoder (entity) {
  DEREncoder.call(this, entity)
  this.enc = 'pem'
}
inherits(PEMEncoder, DEREncoder)

PEMEncoder.prototype.encode = function encode (data, options) {
  const buf = DEREncoder.prototype.encode.call(this, data)

  const p = buf.toString('base64')
  const out = [`-----BEGIN ${options.label}-----`]
  for (let i = 0; i < p.length; i += 64) { out.push(p.slice(i, i + 64)) }
  out.push(`-----END ${options.label}-----`)
  return out.join('\n')
}

module.exports = PEMEncoder