@Nullable
    @Override
    public String handleResponse(Response response) throws IOException {
      return CharStreams.toString(
          new InputStreamReader(response.getBody(), StandardCharsets.UTF_8));
    }
Implementation of {@link RegistryEndpointProvider} for testing.
jib-core/src/test/java/com/google/cloud/tools/jib/registry/RegistryEndpointCallerTest.java