How to use current datetime for FindByTimeValid value in WCF ServiceCertificate config

Question

Hi

How do I use current date & time as the value for the findValue attribute in the ServiceCertificate config when using "FindByTimeValid" for the x509FindType? Using DateTime.Now as below obiously doesn't work but neither does "2010-10-20 14:35:28Z". I have two certificates on the server with the same details as one of them has expired why is why I'm using this find type value.

For example:

<serviceCredentials>
        <serviceCertificate findValue="DateTime.Now" x509FindType="FindByTimeValid" storeLocation="LocalMachine" storeName="My"/>
</serviceCredentials>

Thanks

Keith