KCM: Make the secrets ccache back end configurable, make secrets the default Adds a new option 'ccache_storage' that allows to select either the memory back end or the secrets back end. The secrets back end is the default one and this option is even undocumented. Reviewed-by: Michal Židek <mzidek@redhat.com> Reviewed-by: Simo Sorce <simo@redhat.com>

KCM: Store ccaches in secrets Adds a new KCM responder ccache back end that forwards all requests to sssd-secrets. Reviewed-by: Michal Židek <mzidek@redhat.com> Reviewed-by: Simo Sorce <simo@redhat.com>

KCM: Implement an internal ccache storage and retrieval API In order for the KCM server to work with ccaches stored in different locations, implement a middle-man between the KCM server and the ccache storage. This module has asynchronous API because we can't assume anything about where the ccaches are stored. Reviewed-by: Michal Židek <mzidek@redhat.com> Reviewed-by: Simo Sorce <simo@redhat.com>