use syntax compatible with python before 3.11

Author: prauscher

src/saml2/cert.py

@@ -160,7 +160,7 @@ def create_certificate(
         ])
         builder = builder.subject_name(subject_name)
         if not request:
-            now = datetime.datetime.now(datetime.UTC)
+            now = datetime.datetime.now(datetime.timezone.utc)
             builder = builder.serial_number(
                 sn,
             ).not_valid_before(
@@ -261,7 +261,7 @@ def create_cert_signed_certificate(
             sign_key_str, password=passphrase)
         req_cert = x509.load_pem_x509_csr(request_cert_str)
 
-        now = datetime.datetime.now(datetime.UTC)
+        now = datetime.datetime.now(datetime.timezone.utc)
         cert = x509.CertificateBuilder().subject_name(
             req_cert.subject,
         ).serial_number(
@@ -321,7 +321,7 @@ def verify(self, signing_cert_str, cert_str):
                 cert_str = cert_str.encode("utf-8")
             ca_cert = x509.load_pem_x509_certificate(signing_cert_str)
             cert = x509.load_pem_x509_certificate(cert_str)
-            now = datetime.datetime.now(datetime.UTC)
+            now = datetime.datetime.now(datetime.timezone.utc)
 
             if ca_cert.not_valid_before_utc >= now:
                 return False, "CA certificate is not valid yet."

src/saml2/sigver.py

@@ -389,7 +389,7 @@ def active_cert(key):
     except AttributeError:
         return False
 
-    now = datetime.datetime.now(datetime.UTC)
+    now = datetime.datetime.now(datetime.timezone.utc)
     valid_from = cert.not_valid_before_utc
     valid_to = cert.not_valid_after_utc
     active = valid_from <= now < valid_to