OpenAPI is pretty much everywhere, and having REST services without it for consumers, is pretty much non-existent these days.
Guiced EE provides an out-the-box solution to hosting your OpenAPI servlet.

Your OpenAPI Servlet is now available at /rest/openapi
You can control the OpenAPI rendering through the OpenAPIModule class

The IGuicedSwaggerConfiguration Service Provider exists for you to alter the configuration.
Resources and packages are automatically provided through the RESTContext.getPathServices() method