Multi-Cluster Kubernetes Secrets Management with External Vault Integration

Design a comprehensive secrets management solution for a multi-cluster Kubernetes environment using HashiCorp Vault. Create a Terraform module that dynamically generates short-lived credentials, implements automatic rotation for database and cloud provider credentials, and provides seamless integration with Kubernetes clusters across different regions. Include a custom controller that handles credential synchronization, supports multiple authentication methods (AppRole, Kubernetes auth), and implements robust error handling and retry mechanisms.