@Override
  public KmsClient withDefaultCredentials() throws GeneralSecurityException {
    throw new GeneralSecurityException("TinkeyTestKmsClient has no default credentials");
  }
A client for testing.

<p>The client supports all key uris which start with "tinkey-test-kms-client://" followed by a
JSON-encoded AEAD keyset. It will use this Aead when "getAead" is called. As credentials, it must
be given a file which starts whose contents are "VALID CREDENTIALS".
tools/tinkey/src/main/java/com/google/crypto/tink/tinkey/TinkeyTestKmsClient.java