This function uses the same test as attribute
isExtendedValidation
If isExtendedValidation is true, this function will return
a policy identifier in dotted notation (like 1.2.3.4.5).
If isExtendedValidation is false, this function will return
an empty (length string) value.
A “true” value means:
The object that implements this interface uses a certificate that
was successfully verified as an Extended Validation (EV) cert.
The test is bound to SSL Server Cert Usage.