Quick question about OAuth token refresh rate limits during load testing

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Quick question about handling OAuth token expiration when simulating high-concurrency API traffic from Singapore.

I am running a JMeter 5.6.2 script to test the throughput of the flow configurations endpoint. The goal is to simulate 500 concurrent users fetching flow configurations. Everything works fine for the first 100 requests, but then I start seeing intermittent 401 Unauthorized errors.

I have a JSR223 PreProcessor in JMeter that checks the token expiry and calls /oauth/token to refresh it if needed. However, under load, multiple threads seem to trigger the refresh simultaneously, resulting in a rate limit 429 on the auth endpoint itself. This causes the main test threads to hang waiting for a valid token, skewing the latency metrics completely.

The environment is Genesys Cloud (US-East). I am using a dedicated test tenant for this. The JMeter config uses a simple controller with a loop count of 100 per thread group.

Is there a recommended pattern for managing token refresh in a high-concurrency load test? Should I be using a singleton token manager in JMeter, or is there a specific header or parameter I can use to batch the refresh requests?

Currently, my script looks like this:

  • Thread Group: 500 threads, ramp-up 60 seconds
  • HTTP Request Defaults: Base URL https://api.mypurecloud.com
  • PreProcessor: Checks exp claim in JWT. If exp < now + 60s, calls /oauth/token with grant_type=refresh_token.

The issue is that when 50 threads check the token at the same millisecond, they all decide it’s expired and hit the auth server. This creates a thundering herd problem on the /oauth/token endpoint.

Any advice on how to structure this in JMeter to avoid hitting the auth rate limits while maintaining accurate concurrency simulation? I want to ensure the load test reflects real-world API throughput without being bottlenecked by auth mechanics.

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