fix: force use of TLSv1.3 when IAM auth enabled (#108)

* fix: force use of TLSv1.3 when IAM auth enabled

Author: shubha-rajan

.kokoro/tests/run_tests_windows.sh

@@ -27,6 +27,7 @@ fi
 
 # Add python and pip to PATH
 export PATH=/c/python37:/c/python37/scripts:$PATH
+python --version
 
 # install nox for testing
 pip install --user -q nox

google/cloud/sql/connector/instance_connection_manager.py

@@ -80,6 +80,15 @@ def __init__(self, *args: Any, **kwargs: Any) -> None:
         super(ConnectionSSLContext, self).__init__(*args, **kwargs)
 
 
+class TLSVersionError(Exception):
+    """
+    Raised when the required TLS protocol version is not supported.
+    """
+
+    def __init__(self, *args: Any) -> None:
+        super(TLSVersionError, self).__init__(self, *args)
+
+
 class CloudSQLConnectionError(Exception):
     """
     Raised when the provided connection string is not formatted
@@ -111,8 +120,16 @@ def __init__(
         private_key: bytes,
         server_ca_cert: str,
         expiration: datetime.datetime,
+        enable_iam_auth: bool,
     ) -> None:
         self.ip_addrs = ip_addrs
+
+        if enable_iam_auth and not ssl.HAS_TLSv1_3:  # type: ignore
+            raise TLSVersionError(
+                "Your current version of OpenSSL does not support TLSv1.3, "
+                "which is required to use IAM Authentication."
+            )
+
         self.context = ConnectionSSLContext()
         self.expiration = expiration
 
@@ -293,18 +310,20 @@ async def _get_instance_data(self) -> InstanceMetadata:
         expiration = datetime.datetime.strptime(
             x509.get_notAfter().decode("ascii"), "%Y%m%d%H%M%SZ"
         )
-        if self._credentials is not None:
-            token_expiration: datetime.datetime = self._credentials.expiry
 
-        if expiration > token_expiration:
-            expiration = token_expiration
+        if self._enable_iam_auth:
+            if self._credentials is not None:
+                token_expiration: datetime.datetime = self._credentials.expiry
+            if expiration > token_expiration:
+                expiration = token_expiration
 
         return InstanceMetadata(
             ephemeral_cert,
             metadata["ip_addresses"],
             priv_key,
             metadata["server_ca_cert"],
             expiration,
+            self._enable_iam_auth,
         )
 
     def _auth_init(self) -> None: