UTC-aware datetime/cryptography.x509 modernization; python >= 3.12, cryptography.x509 >= 42.0.0

[jimmbelll]

Description, Motivation and Context

Review these versions carefully.

cryptography.x509 deprecates not_valid_before and not_valid_after, replacing them with the UTC-aware not_valid_before_utc and not_valid_after_utc which were added in 42.0.0.

Further, Python's built-in datetime.datetime.utcnow() is deprecated since 3.12, replaced by now(datetime.UTC). Constant datetime.UTC was added in 3.11.

Further still, x509's not_valid_before_utc/not_valid_after_utc return UTC-aware datetime objects, which don't compare with the UTC-unaware values returned from utcnow(). Comparing the two fails:

TypeError: can't compare offset-naive and offset-aware datetimes

Debian trixie (13.3) stocks python 3.13.5, which motivates these changes.

These warnings indicate that this change is required:

CryptographyDeprecationWarning: Properties that return a naïve datetime object
  have been deprecated. Please switch to not_valid_before_utc.

CryptographyDeprecationWarning: Properties that return a naïve datetime object
  have been deprecated. Please switch to not_valid_after_utc.

Another indication:

>>> x = datetime.datetime.utcnow()
<python-input-3>:1: DeprecationWarning: datetime.datetime.utcnow() is deprecated
  and scheduled for removal in a future version. Use timezone-aware objects to
  represent datetimes in UTC:
    datetime.datetime.now(datetime.UTC).

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.