code: public Blob rotateBlobEncryptionKey(
        String bucketName, String blobName, String oldEncryptionKey, String newEncryptionKey) {
      // [START storageRotateEncryptionKey]
      BlobId blobId = BlobId.of(bucketName, blobName);
      CopyRequest request =
          CopyRequest.newBuilder()
              .setSource(blobId)
              .setSourceOptions(BlobSourceOption.decryptionKey(oldEncryptionKey))
              .setTarget(blobId, BlobTargetOption.encryptionKey(newEncryptionKey))
              .build();
      Blob blob = storage.copy(request).getResult();
      // [END storageRotateEncryptionKey]
      return blob;
    }
docs: [VARIABLE "new_encryption_key"]