[Bug] utils update-authentication-mode fails on no-op updates (Unsupported authentication mode update from X to X) #8903

What were you trying to accomplish?

Re-run eksctl utils update-authentication-mode -f cluster.yml against a cluster whose authentication mode already matches the config file (idempotent re-runs from CI / GitOps pipelines).

What happened?

The command fails hard because it calls UpdateClusterConfig unconditionally, and the EKS API rejects an update where the target mode equals the current mode:

[ℹ]  setting cluster's authentication mode to
Error: failed to update cluster config: operation error EKS: UpdateClusterConfig,
https response error StatusCode: 400, InvalidParameterException:
Unsupported authentication mode update from API_AND_CONFIG_MAP to API_AND_CONFIG_MAP

Note the log line is also broken: setting cluster's authentication mode to prints the --authentication-mode flag value, which is empty when the mode comes from a config file via -f, instead of the mode resolved from the cluster config.

How to reproduce it?

1. Have a cluster with accessConfig.authenticationMode: API_AND_CONFIG_MAP.
2. Put the same mode in cluster.yml.
3. Run eksctl utils update-authentication-mode -f cluster.yml → exits non-zero with the error above.

Expected behavior

When the cluster's authentication mode already equals the desired mode, log something like authentication mode is already API_AND_CONFIG_MAP on cluster X, skipping update and exit 0. The "setting cluster's authentication mode to %s" log should print the actual mode being sent to the API.

Versions

Present on current main (pkg/ctl/utils/update_authentication_mode.go, doUpdateAuthenticationMode).