https://github.com/ServiceStack/ServiceStack.Redis
Edit: for the first time in my life I may be less than correct.
But Redis's authentication is very simple in any case. There's a password. A password, one. That's it. There are no accounts, no usernames, there's no "infrastructure" or any way to hook it into LDAP or other insanity. There's no accounting.
It's not for the kind of authentication ActiveDirectory does. In practice, it's more of an "Oops, did you really mean to connect to that server?" thing.
But I think the guy I was responding to is at least partly wrong, a quick grep through the repo he linked to shows they have everything necessary for authentication, even if it's not as blindingly obvious as in, say, redis-py and redis-rb.
http://stackoverflow.com/questions/8862552/authenticated-ser...