Finally figured out, it's quite simple but i got to look for it with good keywords.
For those who could wonder about the answer, you just declare a variable WebServiceContext in your POJO, with a @Resource annotation.
Example:
@Resource
public WebServiceContext wsCtx;
...
Later:
wsCtx.getUserPrincipal();
Hoping this could help someone later ;)
Have a nice day.
SJ.