Stuck on OAuth2 401 during JMeter load test on EU1

Administration
1

Stuck on OAuth2 401 Unauthorized errors when running a JMeter script against the Genesys Cloud API on our EU1 instance. The environment is Genesys Cloud version 2024.1. We are testing token refresh endpoints to simulate high concurrent agent logins. The script uses 50 threads with a ramp-up of 10 seconds. After 200 requests, we start seeing HTTP 401 responses with the message “Invalid grant”. This happens even though the client credentials are correct and the tokens are valid in the UI. The error rate spikes when the request rate exceeds 10 per second. I suspect this might be related to rate limiting on the OAuth endpoints, but I am not sure. The logs show no clear pattern for the failures. It seems random. I want to ensure our load test setup is correct before proceeding with higher concurrency levels. Any guidance on handling OAuth rate limits in JMeter would be helpful. I have checked the documentation but did not find specific limits for token refresh endpoints.

  • Tried reducing the thread count to 10, which reduces errors but does not eliminate them entirely.
  • Verified that the client ID and secret are correct by testing with a single request manually.
2

The problem is likely that token concurrency limits in EU1 during ramp-up. Check the OAuth rate limits in the documentation. See support article KB-9921 for JMeter token pooling best practices.

3

Have you tried adjusting the JMeter thread group to utilize the Concurrent Thread Group instead of the standard loop? The standard loop often sends requests sequentially per thread, which can create a burst effect that exceeds the OAuth service’s concurrency limits during the ramp-up phase. This is particularly relevant in the EU1 region where rate limiting is strictly enforced to protect platform stability.

The “Invalid grant” error frequently appears when the refresh token is used concurrently by multiple threads before the previous refresh cycle completes. The platform may invalidate the token if it detects overlapping refresh attempts. Switching to a Concurrent Thread Group allows for better control over the actual number of simultaneous requests hitting the authentication endpoint. Additionally, ensure that the token storage is thread-safe within the script.

Check these items:

  • OAuth token concurrency limits
  • JMeter Concurrent Thread Group configuration
  • Token refresh interval settings
  • EU1 regional rate limiting thresholds
4

This happens because the OAuth service enforcing strict concurrency limits during token refresh operations, which JMeter’s standard thread group model often violates due to its burst behavior. The “Invalid grant” error typically indicates that the refresh token has been invalidated because it was consumed or rotated faster than the platform allows, or that the concurrent requests exceeded the rate limit for the specific client ID.

To resolve this, switch from the standard Thread Group to the Concurrent Thread Group in JMeter. This ensures a more realistic and controlled distribution of requests, preventing the sudden spike that triggers the 401s. Additionally, implement a token pooling strategy where tokens are refreshed only when expired, rather than every request.

Here is a sample JSR223 PreProcessor snippet to handle token caching and avoid unnecessary refresh calls:

import org.apache.jmeter.util.JMeterUtils

def tokenManager = JMeterUtils.getPropDefault("oauth_token", null)
if (tokenManager == null || System.currentTimeMillis() > tokenManager.expiryTime) {
 // Trigger refresh logic here
 def newToken = callRefreshEndpoint()
 def props = new Expando()
 props.token = newToken.access_token
 props.expiryTime = System.currentTimeMillis() + (newToken.expires_in * 1000)
 JMeterUtils.setProperty("oauth_token", props)
}
else {
 vars.put("access_token", tokenManager.token)
}

Warning: Ensure your client credentials have the appropriate scopes for high-volume operations. If the issue persists, check the EU1 specific rate limits in the developer portal, as they are stricter than other regions. Also, verify that the refresh tokens are not being shared across threads, as this can lead to immediate invalidation.

For bulk export or audit trail scenarios, this pattern is crucial to maintain chain of custody without triggering security blocks. The documentation on OAuth best practices for load testing provides further details on token rotation strategies.