public Slot? pkcs11_get_trust_store_slot ()
Selects an appropriate PKCS#11 slot to store trust assertions.
The slot to use is normally configured automatically by the system.
This will only return a valid result after the [func@pkcs11_initialize] method has been called.
When done with the Slot, use unref to release it.
the Slot to use for trust assertions, or null if not initialized or no appropriate trust store could be found.