def check_cache(params)
      logger.verbose("TokenRequest checking cache #{@token_cache} for token.")
      result = @cache_driver.find(params)
      logger.info("#{result ? 'Found' : 'Did not find'} token in cache.")
      result
    end
def check_cache(params)
      logger.verbose("TokenRequest checking cache #{@token_cache} for token.")
      result = @cache_driver.find(params)
      logger.info("#{result ? 'Found' : 'Did not find'} token in cache.")
      result
    end
Attempts to fulfill the request from @token_cache.

 @return TokenResponse
   If the cache contains a valid response it wil be returned as a
   SuccessResponse. Otherwise returns nil.