This read-write integer selects, by index, which stored certificate-and-key pair the HTTPS service should use for new sessions going forward, and the write will succeed even if that particular certificate or key doesn't exist yet. An administrator sets this when managing multiple certificate slots, such as switching to a newly imported or regenerated certificate without disrupting currently active sessions. For example, after uploading a new CA-signed certificate to a specific slot, an admin sets this OID to that slot's index so future HTTPS connections use it instead of the old self-signed certificate.