THPDFCSCSignatureProvider.Cancel Method
procedure Cancel(const OperationIdentifier: AnsiString);
override;
Marks one CSC operation as cancelled so that subsequent and in-flight signing work for that identifier stops at the next cancellation point
An empty OperationIdentifier is ignored; otherwise the identifier joins a bounded cancellation list capped by THPDFCSCOptions.MaxOperationCacheEntries, the oldest entries being dropped first
Cancellation is observed before each transport call, between retry attempts and during the short-sliced polling waits, and the identifier is also forwarded to the THPDFCSCTransport callback so the application can abort its own in-flight HTTP request