windowsservercore: urllib SSL errors

I can't get SSL to work in the container, any ideas welcome:

docker run -it python:3.7.1-windowsservercore
>>> import urllib.request; urllib.request.urlopen("https://letsencrypt.org/")
Traceback (most recent call last):
  File "C:\Python\lib\urllib\request.py", line 1317, in do_open
    encode_chunked=req.has_header('Transfer-encoding'))
  File "C:\Python\lib\http\client.py", line 1229, in request
    self._send_request(method, url, body, headers, encode_chunked)
  File "C:\Python\lib\http\client.py", line 1275, in _send_request
    self.endheaders(body, encode_chunked=encode_chunked)
  File "C:\Python\lib\http\client.py", line 1224, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
  File "C:\Python\lib\http\client.py", line 1016, in _send_output
    self.send(msg)
  File "C:\Python\lib\http\client.py", line 956, in send
    self.connect()
  File "C:\Python\lib\http\client.py", line 1392, in connect
    server_hostname=server_hostname)
  File "C:\Python\lib\ssl.py", line 412, in wrap_socket
    session=session
  File "C:\Python\lib\ssl.py", line 853, in _create
    self.do_handshake()
  File "C:\Python\lib\ssl.py", line 1117, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLCertVerificationError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1051)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python\lib\urllib\request.py", line 222, in urlopen
    return opener.open(url, data, timeout)
  File "C:\Python\lib\urllib\request.py", line 525, in open
    response = self._open(req, data)
  File "C:\Python\lib\urllib\request.py", line 543, in _open
    '_open', req)
  File "C:\Python\lib\urllib\request.py", line 503, in _call_chain
    result = func(*args)
  File "C:\Python\lib\urllib\request.py", line 1360, in https_open
    context=self._context, check_hostname=self._check_hostname)
  File "C:\Python\lib\urllib\request.py", line 1319, in do_open
    raise URLError(err)
urllib.error.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1051)>
>>>

Start by reproducing the documented python:3.7.1-windowsservercore command and its urllib request to letsencrypt.org. Investigate the container's certificate trust configuration and verify that the same request succeeds without the reported certificate verification error.