ubuntu-advantage: compare date from two /aware/ datetime objects

The current implementation attempts to compare two datetime objects
by comparing the value returned by .timestamp().

However, one of the objects is an /aware/ datetime and the other is a
/naive/ datetime.

When calling .timestamp() on a naive datetime object, the function
expects the datetime object to represent local time. However, in our
scenario, it was UTC time.

Therefore, the comparison is slightly inaccurate and can end up
rejecting a token that is not yet expired ; or accepting one that is
about to expire.

In practice, this should rarely be a problem (a few hours is not a big
deal). But we now compare two /aware/ datetime objects to make the
comparison more correct.

Also, datetime.datetime.utcnow() (which returns a naive datetime object)
is deprecated in favor of datetime.datetime.now() (which can return an
aware datetime object if timezone information is passed).

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquity/server/ubuntu_advantage.py

@@ -17,6 +17,7 @@ helper. """
 
 import asyncio
 import contextlib
+import datetime
 import json
 import logging
 import os
@@ -331,7 +332,7 @@ class UAInterface:
         # is specified in RFC 3339 but not supported by fromisoformat before
         # Python 3.11. See https://bugs.python.org/issue35829
         expiration = dt.fromisoformat(info["expires"].replace("Z", "+00:00"))
-        if expiration.timestamp() <= dt.utcnow().timestamp():
+        if expiration <= dt.now(datetime.timezone.utc):
             raise ExpiredTokenError(token, expires=info["expires"])
 
         def is_activable_service(service: dict) -> bool: