See also https://github.com/ansible/ansible/issues/31741

Fails on too old pip:

Downloading/unpacking cryptography>=2.1.4 (from
pyOpenSSL->autoca==0.3.2)
  Running setup.py (path:/tmp/pip-build-ZJGhFW/cryptography/setup.py) egg_info for package cryptography
    error in cryptography setup command: Invalid environment marker: platform_python_implementation != 'PyPy'
    Complete output from command python setup.py egg_info:
    error in cryptography setup command: Invalid environment marker: platform_python_implementation != 'PyPy'

The 'digest' argument to OpenSSL.crypto.CRL.export has only been added
in recent versions.

see also e8f12c4b

gnutls fails to consider the certificate valid:

|<2>| error: extensions present in certificate with version 1

found via:

gnutls-cli --debug 99 --x509cafile /etc/ssl/certs/ca-certificates.crt github.com