MDC - Root(Main) Thread

I want to add some values to the SLF4J MDC.

I am currently doinbg this inside a RequestHandler that I add once a Session is created.

Now if I log e.g. something inside my navigator, the MDC values are not present, as it is executed in a different thread.

What would be the correct location/hook to put MDC values to the main/root thread so that they are available everywhere?