sample-plugin: TLS Keying Material Exporter [RFC-5705] demonstration plug-in

sample-plugin: TLS Keying Material Exporter [RFC-5705] demonstration plug-in

A simple plug-in with a corresponding HTTP server and client which can authenticate
an HTTP user based on the authentication already done via an established OpenVPN
connection

[DS: Renamed the module at commit time from sso to keyingmaterialexporter to
     avoid confusion with other Single-Sign-On solutions.  Updated documentation
     and commits accordingly.  Added --pull to the client config]

Signed-off-by: Daniel Kubec <niel@rtfm.cz>
Signed-off-by: David Sommerseth <davids@redhat.com>
Acked-by: David Sommerseth <davids@redhat.com>