Fix serve certificate timezone issue

CHANGELOG.md

@@ -15,6 +15,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Tutorial**:
   - Added a tutorial to the documentation to help new users get started with writing a provider using `tf`.
 
+### Fixed
+
+- Fixed the gRPC server self-signed certificate being generated with `not_valid_before` in the future
+  - This was caused by generating a `datetime` in the local timezone, but `x509` treating it as UTC
+
 ## 1.1.0
 
 ### Added

tf/runner.py

@@ -197,6 +197,8 @@ def _get_cert_cache_path() -> Path:
 def _self_signed_cert() -> Tuple[bytes, Any]:
     """Generate or load cached keypair and cert, return a server credentials object"""
     # Lazy load expensive cryptography imports
+    from datetime import timezone
+
     import grpc
     from cryptography import x509
     from cryptography.hazmat.primitives import hashes, serialization
@@ -213,10 +215,8 @@ def _self_signed_cert() -> Tuple[bytes, Any]:
             # Check if certificate is still valid
             cert_pem = cached["cert_pem"].encode()
             cert = x509.load_pem_x509_certificate(cert_pem)
-            # Compare UTC times
-            from datetime import timezone as tz
 
-            if cert.not_valid_after_utc > datetime.now(tz.utc):
+            if cert.not_valid_after_utc > datetime.now(timezone.utc):
                 # Certificate is still valid, use cached version
                 private_key_pem = cached["key_pem"].encode()
                 cert_chain = base64.b64decode(cached["cert_chain"])
@@ -238,7 +238,7 @@ def _self_signed_cert() -> Tuple[bytes, Any]:
     )
 
     name = x509.Name([x509.NameAttribute(x509.NameOID.COMMON_NAME, "localhost")])
-    now = datetime.now()
+    now = datetime.now(timezone.utc)
 
     # With subject alternative names
     certificate = (