Allow to open "KeychainStore" on macOS as special keystore

[kaikramer]

Similar to #746 this is about being able to open the macOS Keychain in KSE.

There is one KeyStore name defined by the Apple JCA/JCE provider: KeychainStore

Documentation of the Apple provider:
https://docs.oracle.com/en/java/javase/17/security/oracle-providers.html#GUID-3185649A-C316-45F2-A70E-2B3FF6BDC34F

[jonwltn]

I started on this one last year, but never finished up as there was lots of other things to do. I'll add this one to my list of things to do.

[jonwltn]

How far do we want to go with this feature? The Keychain is read-only in that, adding new key pair or certs to Keychain is not possible. Adding a key pair is silently ignored, and adding a trust cert generates an exception stating that Apple tools must be used for importing a cert.

Do we disable the menu items for generating a key pair or importing a trusted cert?

[kaikramer]

Looking into the source code of the Apple provider, changes to the Keychain should be possible. There is an implementation of the store() method in the provider that updates the macOS Keychain.

[jonwltn]

Ah, I see. It's likely the Keychain provider tries to make the Keychain key store act like a file based key store that needs to saved. My expectation was colored by my experience with the Windows-MY key store, which didn't require using the store() method to save the changes.

I will figure it out.