If you want to audit WCF Service, place the below configuration settings in web.config.
<configuration>
<system.serviceModel>
<behaviors>
<behavior>
<serviceSecurityAudit
auditLogLocation="Application"
suppressAuditFailure="true"
serviceAuthorizationAuditLevel="Failure"
messageAuthenticationAuditLevel=
"SuccessOrFailure" />
</behavior>
</behaviors>
</system.serviceModel>
</configuration>
Configure this setting to log security events for success, failure, or both. The events are written to the Windows system event log, and you can view them in the Event Viewer.