This INTEGER lists the specific authentication method in use for this SA, and its description notes broadly that it could be a certificate or a pre-shared key. An admin checks this on a live SA to confirm which authentication mechanism was actually negotiated, which can matter when a policy allows multiple types and the admin needs to verify the stronger one was actually used. For example, an admin auditing security posture might check this field on several active SAs to confirm none of them fell back to a weaker pre-shared-key method when certificate authentication was expected.