chore: lazy init keys with lazy refresh (#1110)

RSA key-pair generation should be done on first connection
attempt when lazy refresh strategy is configured.

google/cloud/sql/connector/connector.py

@@ -108,20 +108,32 @@ def __init__(
                 RefreshStrategy.BACKGROUND ("BACKGROUND").
                 Default: RefreshStrategy.BACKGROUND
         """
+        # if refresh_strategy is str, convert to RefreshStrategy enum
+        if isinstance(refresh_strategy, str):
+            refresh_strategy = RefreshStrategy._from_str(refresh_strategy)
+        self._refresh_strategy = refresh_strategy
         # if event loop is given, use for background tasks
         if loop:
             self._loop: asyncio.AbstractEventLoop = loop
             self._thread: Optional[Thread] = None
-            self._keys: asyncio.Future = loop.create_task(generate_keys())
+            # if lazy refresh is specified we should lazy init keys
+            if self._refresh_strategy == RefreshStrategy.LAZY:
+                self._keys: Optional[asyncio.Future] = None
+            else:
+                self._keys = loop.create_task(generate_keys())
         # if no event loop is given, spin up new loop in background thread
         else:
             self._loop = asyncio.new_event_loop()
             self._thread = Thread(target=self._loop.run_forever, daemon=True)
             self._thread.start()
-            self._keys = asyncio.wrap_future(
-                asyncio.run_coroutine_threadsafe(generate_keys(), self._loop),
-                loop=self._loop,
-            )
+            # if lazy refresh is specified we should lazy init keys
+            if self._refresh_strategy == RefreshStrategy.LAZY:
+                self._keys = None
+            else:
+                self._keys = asyncio.wrap_future(
+                    asyncio.run_coroutine_threadsafe(generate_keys(), self._loop),
+                    loop=self._loop,
+                )
         self._cache: Dict[str, Union[RefreshAheadCache, LazyRefreshCache]] = {}
         self._client: Optional[CloudSQLClient] = None
 
@@ -148,10 +160,6 @@ def __init__(
         if isinstance(ip_type, str):
             ip_type = IPTypes._from_str(ip_type)
         self._ip_type = ip_type
-        # if refresh_strategy is str, convert to RefreshStrategy enum
-        if isinstance(refresh_strategy, str):
-            refresh_strategy = RefreshStrategy._from_str(refresh_strategy)
-        self._refresh_strategy = refresh_strategy
         self._universe_domain = universe_domain
         # construct service endpoint for Cloud SQL Admin API calls
         if not sqladmin_api_endpoint:
@@ -258,6 +266,8 @@ async def connect_async(
             DnsNameResolutionError: Could not resolve PSC IP address from DNS
                 host name.
         """
+        if self._keys is None:
+            self._keys = asyncio.create_task(generate_keys())
         if self._client is None:
             # lazy init client as it has to be initialized in async context
             self._client = CloudSQLClient(

tests/unit/test_connector.py

@@ -114,6 +114,12 @@ def test_Connector_Init(fake_credentials: Credentials) -> None:
         connector.close()
 
 
+def test_Connector_Init_with_lazy_refresh(fake_credentials: Credentials) -> None:
+    """Test that Connector with lazy refresh sets keys to None."""
+    with Connector(credentials=fake_credentials, refresh_strategy="lazy") as connector:
+        assert connector._keys is None
+
+
 def test_Connector_Init_with_credentials(fake_credentials: Credentials) -> None:
     """Test that Connector uses custom credentials when given them."""
     with patch(