Retrofit and envelopes

LoginContextUnwrappingConverter.java

public class LoginContextUnwrappingConverter extends Converter.Factory {
    @Override
    public Converter<ResponseBody, LoginContext>
            responseBodyConverter(Type type,
                                  Annotation[] annotations,
                                  Retrofit retrofit) {
        if (type != LoginContext.class) {
            return null;
        }

        final Converter<ResponseBody, LoginResponse> delegate =
                retrofit.nextResponseBodyConverter(this,
                                                   LoginResponse.class,
                                                   annotations);

        return body -> {
            LoginResponse wrapper = delegate.convert(body);
            return wrapper.context();
        };
    }
}