Auth: Persist session before refreshing current logged in user

[yhabteab]

When using external auth, e.g. NGINX basic auth, it's not possible to use the user's session for Nagvis authentication, even though the cookie path is set to /, which allows another Icinga web instance to access that same cookie. However, as the user's cookie is periodically refreshed, this invalidates the entire session for the third party, resulting in the REMOTE_USER header being empty.

The Application State Controller already does the same thing!

icingaweb2/application/controllers/ApplicationStateController.php

Lines 38 to 40 in cd2daeb

	if ($last + 600 < $now) {
	Session::getSession()->write();
	$params = session_get_cookie_params();

Might fix Icinga/icingaweb2-module-nagvis#35 (I didn't test it as I don't use apache). Using NGINX works fine though. @slalomsk8er can you please verify this if you are still using apache and Nagvis.