Parse, modify and write an x509 certificate with Python (WIP)

modify-x509-cert.py

from cryptography import x509
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives import serialization
import os

# Read cert from file
with open("cert.pem", "rb") as f:
    cert= x509.load_pem_x509_certificate(f.read(), default_backend())

# This causes problems due to `subject` attribute not being writable
# Edit subject entry of the certificate
cert.subject = x509.Name([x509.NameAttribute(x509.NameOID.COMMON_NAME, "example.com")])

# Write cert to file
with open("cert.crt.bak", "wb") as f:
    f.write(cert.public_bytes(encoding=serialization.Encoding.PEM))