Improve client credential server caching

[EricWittmann]

Feature or Problem Description

Currently we cache client credentials grant tokens (for basic auth) for a configurable period of time. If the cache time is greater than the expiration time of the token, then auth can fail.

Proposed Solution

Instead, we should cache the tokens based on their expiration. On a per-token basis. So instead of just a cache timeout, we intelligently remove tokens from the cache before they are set to expire.