Add Password parameter, and change Test-TargetResource to match the Subj...

Add Password parameter, and change Test-TargetResource to match the Subject name, instead of looking for equal to.

This has been tested on Windows 2008R2 and 2012R2.
Passing in a SecureString and decrypting the plain text if needed would be the better choice.  (Though it looks like we'd actually be passing in a PSCredential, since that's what DSC will encrypt for you in the MOF document.  It doesn't know what to do with SecureString objects passed by themselves.)