How can I custom extensions in x.509 cert?

I need add some value in cert extension field, such as add an extension named "num" to indicate something's count. But it seems we can only add some standard extension type which is defined with registed oid. If there is a way to custom a new extension type or creat a map between my new oid and the registed extension oid

  File "C:\Users\xm\AppData\Local\Programs\Python\Python310\lib\site-packages\cryptography\x509\base.py", l开发者_运维百科ine 885, in sign
    return rust_x509.create_x509_certificate(self, private_key, algorithm)
NotImplementedError: Extension not supported: 1.1.1.1