Use timezone-aware objects to represent datetimes in UTC.

sros2/sros2/_utilities.py

@@ -80,7 +80,7 @@ def build_key_and_cert(subject_name, *, ca=False, ca_key=None, issuer_name=''):
     else:
         extension = x509.BasicConstraints(ca=False, path_length=None)
 
-    utcnow = datetime.datetime.utcnow()
+    utcnow = datetime.datetime.now(datetime.UTC)
     builder = x509.CertificateBuilder(
         ).issuer_name(
             issuer_name

sros2/test/sros2/commands/security/verbs/test_create_enclave.py

@@ -71,6 +71,8 @@ def check_common_name(entity, expected_value):
 
 def _datetimes_are_close(actual, expected):
     # We can't check exact times, but an hour's resolution is fine for testing purposes
+    actual = actual.replace(tzinfo=datetime.timezone.utc)
+    expected = expected.replace(tzinfo=datetime.timezone.utc)
     return actual <= expected and actual >= (expected - datetime.timedelta(hours=1))
 
 
@@ -122,7 +124,7 @@ def test_cert_pem(enclave_keys_dir):
     assert isinstance(cert.signature_hash_algorithm, hashes.SHA256)
 
     # Verify the cert is valid for the expected timespan
-    utcnow = datetime.datetime.utcnow()
+    utcnow = datetime.datetime.now(datetime.UTC)
 
     # Using a day earlier here to prevent Connext (5.3.1) from complaining
     # when extracting it from the permissions file and thinking it's in the future