Part 5 defines the securityRejectedSessionCount as part of the ServerDiagnosticsSummaryDataType, with the following description: "The number of client session establishment requests (ActivateSession and CreateSession) that were rejected due to security constraints since the server was started (or restarted).". However it should be clarified what exactly the "security constraints" are, like always when the ActivateSession or CreateSession service returns Bad_UserAccessDenied or Bad_SecurityChecksFailed which is the case when an invalid password was provided or some signature check failed.