feat(core): add KeyAuth.close() to stop the token refresh thread

Each KeyAuth started a daemon thread that refreshed tokens forever, with
no way to stop it, so a discarded instance kept running and requesting
tokens. close() stops the loop, shuts down the refresh executor and
removes the atexit hook. It is safe to call more than once.

Author: mittalpk

CHANGELOG.md

@@ -1,6 +1,8 @@
 ## Release (2026-MM-DD)
 
 - `core`:
+  - [v0.4.0](core/CHANGELOG.md#v040)
+    - **Feature:** Add `KeyAuth.close()` to stop the background token refresh thread and its worker, so a discarded instance no longer keeps running and requesting tokens
   - [v0.3.1](core/CHANGELOG.md#v031)
     - **Fix:** Refresh access tokens five minutes before expiration instead of after, and wait for in-progress refreshes before authorizing requests
 - `alb`:

core/CHANGELOG.md

@@ -1,3 +1,6 @@
+## v0.4.0
+- **Feature:** Add `KeyAuth.close()` to stop the background token refresh thread and its worker, so a discarded instance (for example after key rotation) no longer keeps running and requesting tokens
+
 ## v0.3.1
 - **Fix:** Refresh access tokens five minutes before expiration instead of after, and wait for in-progress refreshes before authorizing requests
 

core/pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "stackit-core"
-version = "v0.3.1"
+version = "v0.4.0"
 description = "Core functionality for the STACKIT SDK for Python"
 authors = [{ name = "STACKIT Developer Tools", email = "developer-tools@stackit.cloud" }]
 requires-python = ">=3.10,<4.0"

core/src/stackit/core/auth_methods/key_auth.py

@@ -54,6 +54,8 @@ class KeyAuth(AuthBase):
     executor: ThreadPoolExecutor
     refresh_future: Optional[futures.Future]
     service_account_key: ServiceAccountKey
+    _stop: threading.Event
+    _refresh_thread: Optional[threading.Thread]
 
     def __init__(
         self,
@@ -66,6 +68,8 @@ def __init__(
         self.executor = ThreadPoolExecutor(max_workers=1)
         self.access_token = None
         self.refresh_future = None
+        self._stop = threading.Event()
+        self._refresh_thread = None
         self.__create_initial_token()
         self.__fetch_token_from_endpoint()
         self.__start_token_refresh_task()
@@ -92,6 +96,21 @@ def __call__(self, r: Request) -> Request:
             r.headers["Authorization"] = f"Bearer {self.access_token}"
         return r
 
+    def close(self) -> None:
+        """Stop the background token refresh and release its worker.
+
+        Call this when the instance is no longer needed, for example after
+        replacing it during key rotation in a long-running process. Without it
+        the refresh thread keeps running and keeps requesting tokens. Safe to
+        call more than once.
+        """
+        self._stop.set()
+        self.executor.shutdown(wait=False, cancel_futures=True)
+        atexit.unregister(self.__shutdown)
+        thread = self._refresh_thread
+        if thread is not None and thread is not threading.current_thread():
+            thread.join()
+
     def __create_initial_token(self) -> None:
         payload = {
             "iss": self.service_account_key.credentials.issuer,
@@ -126,8 +145,7 @@ def __fetch_token_from_endpoint(self) -> None:
 
     def __start_token_refresh_task(self):
         def token_refresh_task():
-            while True:
-                time.sleep(self.TOKEN_EXPIRY_CHECK_INTERVAL.total_seconds())
+            while not self._stop.wait(self.TOKEN_EXPIRY_CHECK_INTERVAL.total_seconds()):
                 with self.lock:
                     if self.refresh_future is not None and self.refresh_future.done():
                         self.refresh_future.result()
@@ -139,6 +157,7 @@ def token_refresh_task():
         thread = threading.Thread(target=token_refresh_task)
         thread.daemon = True
         thread.start()
+        self._refresh_thread = thread
 
     def __refresh_token(self):
         with self.lock:

core/tests/core/test_auth.py

@@ -2,6 +2,9 @@
 from pathlib import Path, PurePath
 from threading import Event, Lock, Thread
 
+import time
+from datetime import timedelta
+
 import pytest
 import json
 import jwt
@@ -382,3 +385,61 @@ def result(self):
 
         assert not call_thread.is_alive()
         assert request.headers["Authorization"] == f"Bearer {fresh_token}"
+
+
+class TestKeyAuthClose:
+    """A discarded KeyAuth must be able to stop its background token refresh."""
+
+    @staticmethod
+    def _make_auth(service_account_key_file_json, mock_post, access_token):
+        service_account_key = ServiceAccountKey.model_validate_json(service_account_key_file_json)
+        service_account_key.credentials.private_key = "test-private-key"
+        response = Mock()
+        response.raise_for_status.return_value = None
+        response.json.return_value = {
+            "access_token": access_token,
+            "refresh_token": jwt.encode({"exp": 4102444800}, "secret", algorithm="HS256"),
+        }
+        mock_post.return_value = response
+        return KeyAuth(service_account_key)
+
+    def test_close_stops_the_refresh_thread_and_further_token_requests(self, service_account_key_file_json):
+        def set_initial_token(auth):
+            auth.initial_token = "test-initial-token"
+
+        expired = jwt.encode({"exp": 1}, "secret", algorithm="HS256")
+        with (
+            patch.object(KeyAuth, "_KeyAuth__create_initial_token", new=set_initial_token),
+            patch.object(KeyAuth, "TOKEN_EXPIRY_CHECK_INTERVAL", timedelta(milliseconds=10)),
+            patch("requests.post") as mock_post,
+        ):
+            # An access token that is always expired keeps the refresh loop busy.
+            auth = self._make_auth(service_account_key_file_json, mock_post, expired)
+            thread = auth._refresh_thread
+            assert thread is not None and thread.is_alive()
+
+            auth.close()
+
+            assert not thread.is_alive()
+            requests_after_close = mock_post.call_count
+            time.sleep(0.1)  # ten refresh intervals
+            assert mock_post.call_count == requests_after_close
+
+    def test_close_is_idempotent(self, service_account_key_file_json):
+        def set_initial_token(auth):
+            auth.initial_token = "test-initial-token"
+
+        valid = jwt.encode({"exp": 4102444800}, "secret", algorithm="HS256")
+        with (
+            patch.object(KeyAuth, "_KeyAuth__create_initial_token", new=set_initial_token),
+            patch("requests.post") as mock_post,
+            patch("stackit.core.auth_methods.key_auth.atexit") as mock_atexit,
+        ):
+            auth = self._make_auth(service_account_key_file_json, mock_post, valid)
+
+            auth.close()
+            auth.close()
+
+            assert not auth._refresh_thread.is_alive()
+            assert auth.executor._shutdown
+            mock_atexit.unregister.assert_called_with(auth._KeyAuth__shutdown)