code: public JwkProviderBuilder rateLimited(long bucketSize, long refillRate, TimeUnit unit) {
          bucket = new BucketImpl(bucketSize, refillRate, unit);
          return this;
      }
docs: Enable the cache specifying size and expire time.
  
  @param bucketSize max number of jwks to deliver in the given rate.
  @param refillRate amount of time to wait before a jwk can the jwk will be cached
  @param unit       unit of time for the expire of jwk
  @return the builder