JAAS and web service authorization : get logged user

I've a JSF application that do login via JAAS. It works fine.

Now, my page calls a REST web service. I need to know who did the request.

In the request's header I have:

Cookie = JSESSIONID=XBHZuYnzgkGyQSR8kBLNSks_s7nuXAMli7Gp-9Mn.dlicitra; _ga=GA1.1.1590792307.1560863707

The web service is implemented in a Stateless EJB. The method is:

@Path(value = "myservice/{id}")
@GET
@Produces(value = "application/json")
public List<Records> getServices(
        @HeaderParam(value = "Cookie") String cookie,
        @PathParam(value = "id") Long id){
    return ... ;
}

How can I get the logged user from the cookie string?

Solution

As explained in the comment, instead of mangling with parsing or decoding the cookie's SessionId, I'd go with the Java EE's security API built-in solution of injecting the SecurityContext into the EJB, and getting the userPrincipal from it:

@Context
private SecurityContext securityContext;

And in your method:

Principal principal = securityContext.getUserPrincipal();