code: func CacheAuthorization(a Authorizer, expiration time.Duration) Authorizer {
  	cache := cache.New(expiration, 30*time.Second)
  
  	return &cachedAuthorizer{
  		Authorizer: a,
  		cache:      cache,
  	}
  }
docs: // CacheAuthorization wraps an Authorizer in an in memory cache that expires
  // after the given expiration. Only positive authorizations will be cached.