When user right click on any menu from web portal and select that "Open in new tab", at that time system must redirect user to login page and ask login credentials again. So there can be 2 different or same users may be logged in in same browser.
Browser doesn’t differentiate tabs vs working in the same tab i.e. session is shared, cookies are shared so you need to invent something like passing a parameter with session ID around and, based on it, logging different user in. I’d avoid it though because it’s potential security issue.