Package-level declarations

A ChallengeChecker that checks a list of ChallengeCheckers in order.

A basic implementation of ChallengeChecker that checks if the challenge in the attestation certificate is equal to the expected challenge.

A ChallengeChecker which checks for replay of challenges via an in-memory LRU cache which holds up to maxCacheSize challenges. Challenges are considered invalid if they are already present in the cache, which prevents replay (reuse of challenges). Checking a challenge will affect the ordering of the cache, making it more-recently-used.