code: public static VariantStreamIterator enforceShardBoundary(OfflineAuth auth,
        StreamVariantsRequest request, Requirement shardBoundary, String fields) throws IOException,
        GeneralSecurityException {
      return VariantStreamIterator.enforceShardBoundary(GenomicsChannel.fromOfflineAuth(auth, fields),
          request, shardBoundary, fields);
    }
docs: Create a stream iterator that can enforce shard boundary semantics.
  
  @param auth The OfflineAuth to use for the request.
  @param request The request for the shard of data.
  @param shardBoundary The shard boundary semantics to enforce.
  @param fields Which fields to include in a partial response or null for all.
  @throws IOException
  @throws GeneralSecurityException