Can somebody help me with information about KERB_SMART_CARD_LOGON structure defined in NTSecAPI.h?

typedef struct _KERB_SMART_CARD_LOGON {
KERB_LOGON_SUBMIT_TYPE MessageType;
UNICODE_STRING Pin;
ULONG CspDataLength;
PUCHAR CspData;
} KERB_SMART_CARD_LOGON, *PKERB_SMART_CARD_LOGON;


What represent "CspData" field? In MSDN files, I don't find any information about this subject.