Returns the id of the session to acquire. <p/> Acquiring sessions by ID only is a suitable strategy when sessions are natively managed by Shiro directly. For example, the Servlet specification does not have an API that allows session acquisition by session ID, so the session ID alone is not sufficient for ServletContainer-based SessionManager implementations.
A {@code SessionKey} is a key that allows look-up of any particular {@link hunt.shiro.session.Session Session} instance. This is not to be confused what is probably better recognized as a session <em>attribute</em> key - a key that is used to acquire a session attribute via the {@link hunt.shiro.session.Session#getAttribute(Object) Session.getAttribute} method. A {@code SessionKey} looks up a Session object directly. <p/> While a {@code SessionKey} allows lookup of <em>any</em> Session that might exist, this is not something in practice done too often by most Shiro end-users. Instead, it is usually more convenient to acquire the currently executing {@code Subject}'s session via the {@link hunt.shiro.subject.Subject#getSession} method. This interface and its usages are best suited for framework development.