Add fallback for Certificate.not_valid_before/after_utc

The Certificate.not_valid_before/after_utc is only available in
Python Cryptography 42 or later. If the system does not have
this version, it will use Certificate.not_valid_before/after and
convert it to UTC.

base/common/python/pki/nssdb.py

@@ -31,6 +31,7 @@
 import stat
 import subprocess
 import tempfile
+import datetime
 import grp
 import pwd
 
@@ -2099,8 +2100,22 @@ def get_cert_info(self, nickname, token=None):
         cert['issuer'] = pki.convert_x509_name_to_dn(cert_obj.issuer)
         cert['subject'] = pki.convert_x509_name_to_dn(cert_obj.subject)
 
-        cert['not_before'] = self.convert_time_to_millis(cert_obj.not_valid_before_utc)
-        cert['not_after'] = self.convert_time_to_millis(cert_obj.not_valid_after_utc)
+        if hasattr(a, 'not_valid_before_utc'):
+            # only available in Python Cryptography 42 or later
+            not_before = cert_obj.not_valid_before_utc
+        else:
+            # convert to UTC
+            not_valid_before = cert_obj.not_valid_before.replace(tzinfo=datetime.timezone.utc)
+        cert['not_before'] = self.convert_time_to_millis(not_before)
+
+        if hasattr(a, 'not_valid_after_utc'):
+            # only available in Python Cryptography 42 or later
+            not_after = cert_obj.not_valid_after_utc
+        else:
+            # convert to UTC
+            not_after = cert_obj.not_valid_after.replace(tzinfo=datetime.timezone.utc)
+        cert['not_after'] = self.convert_time_to_millis(not_after)
+
         cert['trust_flags'] = self.get_trust(nickname=nickname, token=token)
 
         logger.debug('NSSDatabase.get_cert_info(%s) ends', nickname)
@@ -2109,6 +2124,13 @@ def get_cert_info(self, nickname, token=None):
 
     @staticmethod
     def convert_time_to_millis(date):
+        '''
+        Do not use the following code:
+          epoch = datetime.datetime.utcfromtimestamp(0)
+          return (date - epoch).total_seconds() * 1000
+        since it will fail with the following error message:
+          TypeError: can't subtract offset-naive and offset-aware datetimes
+        '''
         return date.timestamp() * 1000
 
     def export_cert_from_db(self,