HashiCorp Vault background credential refresh for mcp_oauth

AI Impact Summary

Background credential refresh support for Vault credentials used by mcp_oauth enables automatic renewal without manual re-auth. This decreases risk of service outages caused by expired leases and improves uptime for applications relying on Vault for dynamic secrets. To operationalize, verify Vault lease TTLs and renewal configuration for mcp_oauth, ensure clients can handle credential rotation with minimal latency, and monitor renewal events.