code: public static void clearInvalidSessions(final Principal user) {
  
  		logger.info("Clearing invalid sessions for user {} ({})", user.getName(), user.getUuid());
  
  		final PropertyKey<String[]> sessionIdKey = StructrApp.key(Principal.class, "sessionIds");
  		final String[] sessionIds                = user.getProperty(sessionIdKey);
  
  		if (sessionIds != null && sessionIds.length > 0) {
  
  			final SessionCache sessionCache = Services.getInstance().getService(HttpService.class).getSessionCache();
  
  			for (final String sessionId : sessionIds) {
  
  				HttpSession session = null;
  				try {
  					session = sessionCache.get(sessionId);
  
  				} catch (Exception ex) {
  					logger.warn("Unable to retrieve session " + sessionId + " from session cache:", ex);
  				}
  
  				if (session == null || SessionHelper.isSessionTimedOut(session)) {
  					SessionHelper.clearSession(sessionId);
  				}
  			}
  		}
  	}
docs: Remove old sessionIds of the given user
  
  @param user