Convert the certificate.p12 that Plex provides to pem format.

plex2pem.py

#!/usr/bin/python

import sys
import hashlib
from OpenSSL.crypto import *

def main():
  if(len(sys.argv) != 3):
    print sys.argv[0] + " /path/to/file.p12 ProcessedMachineIdentifier"
    sys.exit(0)
  hash = hashlib.sha512()
  hash.update('plex')
  hash.update(sys.argv[2])
  passphrase = hash.hexdigest()

  with open(sys.argv[1], 'rb') as f:
    c = f.read()

  p = load_pkcs12(c, passphrase)

  certificate = p.get_certificate()
  private_key = p.get_privatekey()

  type_ = FILETYPE_PEM

  key = dump_privatekey(type_, private_key)
  cert = dump_certificate(type_, certificate)

  print(key + cert)

if __name__ == '__main__':
  main()