Prefer certifi provided certificates (#108)

Sets the SSL context to use the certifi provided root certificate bundle by default, unless the certifi module is older than a year.

If the system-provided root certificate bundle is empty, certifi certs are always loaded.

oyoyo/client.py

@@ -21,6 +21,7 @@ import ssl
 import socket
 import select
 import logging
+import datetime
 import traceback
 
 from oyoyo.parse import parse_raw_irc_command
@@ -207,23 +208,35 @@ class IRCClient:
 
     def get_ssl_context(self):
         """Returns an SSL context for connecting over SSL/TLS.
-        Loads the certifi certs instead of the system-provided certificates if
-        the system certificate store is empty."""
-        context = ssl.create_default_context()
-        # Check if store is empty
-        empty_cert_store = list(context.cert_store_stats().values()).count(0) == 3
-        if empty_cert_store and "certifi" in sys.modules:
-            # Can't validate certificates if store is empty,
-            # load root certificates from certifi instead.
-            context = ssl.create_default_context(cafile=certifi.where())
+        Loads the certifi root certificate bundle if the certifi module is less
+        than a year old or if the system certificate store is empty.
+
+        The cert store on Windows also seems to have issues, so it's better
+        to use the certifi provided bundle assuming it's a recent version.
+
+        On MacOS the system cert store is usually empty, as Python does not use
+        the system provided ones, instead relying on a bundle installed with the
+        python installer."""
+        default_context = ssl.create_default_context()
+        if "certifi" not in sys.modules:
+            return default_context
+
+        # Get age of certifi module
+        certifi_date = datetime.datetime.strptime(certifi.__version__, "%Y.%m.%d")
+        current_date = datetime.datetime.now()
+        certifi_age = current_date - certifi_date
+
+        empty_cert_store = (
+            list(default_context.cert_store_stats().values()).count(0) == 3
+        )
+        # 31557600 seconds is approximately 1 year
+        if empty_cert_store or certifi_age.total_seconds() <= 31557600:
             PchumLog.info(
                 "Using SSL/TLS context with certifi-provided root certificates."
             )
-        else:
-            PchumLog.info(
-                "Using SSL/TLS context with system-provided root certificates."
-            )
-        return context
+            return ssl.create_default_context(cafile=certifi.where())
+        PchumLog.info("Using SSL/TLS context with system-provided root certificates.")
+        return default_context
 
     def connect(self, verify_hostname=True):
         """initiates the connection to the server set in self.host:self.port