If when setting up ActionCable with a Redis backend, you run into the NOAUTH Authentication Required. (Redis::CommandError) issue, you need to modify your cable.yml to fix this issue.
Change the url section to read something like url: "redis://:password@hostname:6379". The key is the colon _before_ the password. It’s basically saying that the username is blank.
I spent way too long banging my head against this. I hope it helps someone else.