[undertow-dev] How to Access ServletContext?

I've embedded Undertow into a Resteasy (JAX-RS) app. One of the libraries I'm using requires a servlet context attribute to be set. How can/should I go about doing so? If I should use a ServletExtension, to clarify, I need to create a file named "io.undertow.servlet.ServletExtension" and put it in the "META-INF/services/" directory? Within the above mentioned file do I need to provide the fully qualified name of the implementation class? Thanks. Best, Ari