Implement barbican memcache security strategy

Provides an option to authenticate and optionally encrtypt the token
data stored in the cache:
memcache_security_strategy = MAC/ENCRTYPT
memcache_secret_key = secret_key

Change-Id: Ia16c8b3d9e3089d9add49e641af0f6668fc7d87f
Related-Prod: PROD-22099
3 files changed