Flask OAuth2 client_credentials token rotation race condition

Why does this config cause intermittent 401 Unauthorized errors during secret rotation?

I am implementing a zero-downtime rotation for our Genesys Cloud OAuth client secrets in a FastAPI microservice. The goal is to update the client_secret in our configuration store without restarting the service or dropping active requests. I am using python-oauth2 with a custom token cache.

The documentation states: “The client_credentials grant type is suitable for server-to-server communication where no user context is required.” However, when I update the secret in the database and trigger a refresh, I see a race condition where requests using the old token fail with 401 Unauthorized before the new token is fully cached.

Here is my current configuration and refresh logic:

oauth:
 provider: genesys_cloud
 client_id: "my-app-client-id"
 client_secret: "old-secret-value"
 token_url: "https://api.mypurecloud.com/oauth/token"
 scopes:
 - "conversation:read"
 - "analytics:read"

import httpx
import time
from fastapi import FastAPI
from oauthlib.oauth2 import BackendApplicationClient
from requests_oauthlib import OAuth2Session

app = FastAPI()

# Global session holder
oauth_session = None

def get_oauth_session():
 global oauth_session
 if oauth_session is None or time.time() > oauth_session.expires_at:
 client = BackendApplicationClient(client_id="my-app-client-id")
 # This block is not thread-safe
 oauth_session = OAuth2Session(client=client)
 oauth_session.fetch_token(
 token_url="https://api.mypurecloud.com/oauth/token",
 username="my-app-client-id",
 password="new-secret-value" # Updated secret
 )
 return oauth_session

When I deploy the new secret, the fetch_token call succeeds, but concurrent requests sometimes grab the None or expired session object before it is re-assigned, leading to failures. The requests_oauthlib library does not seem to handle concurrent token refreshes gracefully in this global scope.

Is there a recommended pattern for thread-safe token rotation in Python that avoids this race condition? I need to ensure that the old token remains valid until the new one is fully cached, or that all requests wait for the refresh to complete without blocking the entire event loop.

This happens because the concurrent access to the token cache during the secret rotation window. When your configuration store updates the client_secret, the existing PureCloudPlatformClientV2 instances in memory still hold the old credentials until they are explicitly refreshed or recreated. The race condition occurs when a request initiates a token refresh using the new secret while another concurrent request attempts to use the stale token or triggers a simultaneous refresh with the old secret, leading to intermittent 401 Unauthorized errors.

To resolve this in a Terraform-managed deployment, you must implement a thread-safe token provider that serializes refresh operations. Do not rely on the default SDK caching for high-concurrency rotation scenarios. Instead, use a singleton pattern with a mutex lock for the token acquisition.

1. Implement a Mutex: Wrap the get_token() method in a lock to ensure only one thread refreshes the token at a time.
2. Force Cache Invalidation: Upon detecting a configuration change in Terraform, trigger a manual cache purge before the new secret is active.
3. Verify Scopes: Ensure your platformClient.auth.client_credentials call includes all necessary scopes, such as analytics:events:read and users:read, as defined in the Genesys Cloud OAuth2 Documentation.

import threading
from purecloudplatformclientv2 import Configuration, PlatformClient

class SafeTokenProvider:
 def __init__(self, client_id, client_secret, org_id):
 self.lock = threading.Lock()
 self.config = Configuration()
 self.config.client_id = client_id
 self.config.client_secret = client_secret
 self.config.org_id = org_id
 self.platform_client = PlatformClient(self.config)

 def get_platform_client(self):
 with self.lock:
 # Force refresh if token is nearing expiration or invalid
 self.platform_client.auth.refresh_access_token()
 return self.platform_client

This approach ensures that token rotation is atomic and prevents concurrent requests from competing for invalid credentials. Always validate your Terraform outputs to confirm the secret update completes before the application picks up the new value.