Fix extracting dates from certificates using UTCTime

sleekxmpp/xmlstream/cert.py

@@ -1,5 +1,5 @@
 import logging
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, tzinfo
 
 # Make a call to strptime before starting threads to
 # prevent thread safety issues.
@@ -32,6 +32,17 @@ class CertificateError(Exception):
     pass
 
 
+class UTC(tzinfo):
+    def utcoffset(self, dt):
+        return timedelta(0)
+    def tzname(self, dt):
+        return "UTC"
+    def dst(self, dt):
+        return timedelta(0)
+
+utc = UTC()
+
+
 def decode_str(data):
     encoding = 'utf-16-be' if isinstance(data, BMPString) else 'utf-8'
     return bytes(data).decode(encoding)
@@ -107,12 +118,12 @@ def extract_dates(raw_cert):
     validity = tbs.getComponentByName('validity')
 
     not_before = validity.getComponentByName('notBefore')
-    not_before = str(not_before.getComponent())
-    not_before = datetime.strptime(not_before, '%Y%m%d%H%M%SZ')
+    not_before = not_before.getComponent().asDateTime
+    not_before = not_before.astimezone(utc).replace(tzinfo = None)
 
     not_after = validity.getComponentByName('notAfter')
-    not_after = str(not_after.getComponent())
-    not_after = datetime.strptime(not_after, '%Y%m%d%H%M%SZ')
+    not_after = not_after.getComponent().asDateTime
+    not_after = not_after.astimezone(utc).replace(tzinfo = None)
 
     return not_before, not_after