The idea with client certificates is that they'll live in a secure keychain and never leave it. The API exposed by whatever manages them will expose functions o

The idea with client certificates is that they'll live in a secure keychain and never leave it. The API exposed by whatever manages them will expose functions of the key (authenticate, encrypt) but not the key itself. If the implementation is decent, you'll authenticate every request, so it isn't possible for requests to be forged or credentials stolen unless you've got a vector to attack the OS's keychain.