Hello,
if you have non-unique SubjectNames in one PKI CA structure you have a problem, which should be solved on the PKI side.
But there is an option for GSS (ClientNameSource) which can be configured for Subject Alternative Names, as example the value "AltNameUPN" for the UPN subject alternative name.
The configuration files are part of the Secure Login Library package but the CommonCryptoLib will be delivered without them. Please check the Secure Login Library package under defaults.
best regards
Alexander Gimbel