craft.session
 You can get info about the active HTTP session with craft.session.
#Properties
The following properties are available:
#isLoggedIn
 Returns whether a user is currently logged in.
{% if craft.session.isLoggedIn %}
  <a href="{{ logoutUrl }}">Logout</a>
{% endif %}
(Note that checking for currentUser works just as well for this.)
#rememberedUsername
 Alias of getRememberedUsername()
#returnUrl
 Alias of getReturnUrl()
#Methods
The following methods are available:
#getFlash( key, defaultValue, delete )
 Returns a flash message by its key, or the default value if that flash message doesn’t exist. Pass false as the third parameter if you don’t want it deleted right away.
#getFlashes( delete )
 Returns any flash messages that have been queued up for the user. Pass false if you don’t want them to be deleted right away.
#getRememberedUsername()
 Returns the user’s username, even if they are not logged in, if they have logged in recently enough for Craft to still remember it.
<input type="text" name="loginName" value="{{ craft.session.getRememberedUsername() }}">
#getReturnUrl()
 Returns the URL the user was trying to access before getting sent to the login page, because they hit a requireLogin tag.
#hasFlash()
 Returns whether a flash message exists, by a given key.