If given, the selectClientCertificates operates on this
list. Otherwise, obtains the list of all certificates from the platform's
certificate stores that are available to this extensions.
Entries that the extension doesn't have permission for or which doesn't
match the request, are removed.
If true, the filtered list is presented to the user to manually select a
certificate and thereby granting the extension access to the
certificate(s) and key(s). Only the selected certificate(s) will be
returned. If is false, the list is reduced to all certificates that the
extension has been granted access to (automatically or manually).