*Issue:* The on-call engineer had to manually diagnose that a Kinesis key rotation was the cause of `HTTP 500` errors on authentication requests, as this information was not available in any runbook.
*Corrective Action:* Update the primary on-call runbook to include a troubleshooting guide for authentication failures. This guide should list potential causes like credential rotation or logging failures, along with commands and dashboard links to investigate each one.
*Result:* This will decrease the time it takes for an on-call engineer to diagnose and resolve common critical errors.