Rotating OAuth client secrets with Flask session persistence issues

Hey everyone, I’ve run into a really strange issue with our internal FastAPI service that caches Genesys Cloud access tokens. We are trying to implement a zero-downtime secret rotation strategy as recommended in the security best practices, but the cached token validation fails immediately after the rotation.

The documentation states: “To rotate a client secret without interrupting active sessions, create a new secret first, then update your application’s configuration to use the new secret for subsequent token requests. The old secret remains valid for a grace period.”

My Python code handles the token refresh like this:

import requests
import time

TOKEN_URL = "https://api.mypurecloud.com/oauth/token"

async def refresh_token(client_id, client_secret):
 payload = {
 "grant_type": "client_credentials",
 "scope": "conversation:read user:read"
 }
 headers = {"Content-Type": "application/json"}
 # Using HTTPBasicAuth for client credentials
 auth = (client_id, client_secret)
 
 response = requests.post(TOKEN_URL, data=payload, headers=headers, auth=auth)
 
 if response.status_code != 200:
 raise Exception(f"Token refresh failed: {response.status_code} - {response.text}")
 
 return response.json()["access_token"]

I have two secrets configured in Genesys Cloud: secret_old and secret_new. I switched my app config to use secret_new at 14:00 CET. The token request succeeds and returns a valid JWT. However, when my background worker uses this new token to call GET /api/v2/users/me at 14:05 CET, it returns:

“error”: “invalid_grant”, “error_description”: “The access token provided is not valid for the requested resource.”

If I wait until 15:00 CET (after the old secret’s grace period supposedly ends), the new token works. But during the overlap, the new token seems to be flagged as invalid by some internal state check.

Is there a specific header or claim I need to include in the initial token request to force the gateway to recognize the new secret’s validity immediately? The docs mention a grace period but do not specify if there is a propagation delay for the new secret’s signing key distribution.

Check your token refresh logic to ensure it does not rely on session-bound state that persists across secret rotations. When rotating secrets, the old token remains valid until expiration, but any refresh attempt using the new secret with an old refresh token structure might fail if the implementation is too rigid. A robust approach uses the client credentials flow for service-to-service calls, avoiding refresh tokens entirely. This eliminates the dependency on session persistence for secret rotation. Here is how you can structure the token fetch in Rust using reqwest to handle the rotation seamlessly by always fetching a new token with the current active secret.

use reqwest::Client;

async fn get_gc_token(client_id: &str, client_secret: &str) -> Result<String, reqwest::Error> {
 let client = Client::new();
 let response = client.post("https://api.mypurecloud.com/oauth/token")
 .header("Content-Type", "application/x-www-form-urlencoded")
 .form(&[
 ("grant_type", "client_credentials"),
 ("client_id", client_id),
 ("client_secret", client_secret),
 ])
 .send()
 .await?
 .json::<serde_json::Value>()
 .await?;
 
 response["access_token"].as_str().unwrap().to_string()
}

This method ensures that every request uses the latest configured secret, effectively bypassing session state issues during rotation.