My company developed a custom Key Storage Provider for Microsoft CAPI so that CNG-using Windows apps can perform signatures using a remote signature service.
I would like to know if there is support in Apple Security framework for a custom module for MacOS that performs a similar task as the KSP on Windows.
The high-level vision would be that an application that signs using keys/certificates stored in the system keychain would be able to sign data using this custom module. I know that for certificates with a private key stored in a smartcard this is possible, e.g. for the Belgian or Estonian eID card
I only found some promising references in old CDSA/CSSM documentation but I'm assuming that this architecture/framework is now deprecated for a long time...