O Guia Definitivo do Yii 1.1

Now that we have seen an example of creating a user identity, we use this to help ease
the implementation of our needed login and logout actions. The following code
demonstrates how this is accomplished:
// Login a user with the provided username and password.
$identity=new UserIdentity($username,$password);
if($identity->authenticate())
Yii::app()->user->login($identity);
else
echo $identity->errorMessage;
......
// Logout the current user
Yii::app()->user->logout();
Here we are creating a new UserIdentity object and passing in the authentication
credentials (i.e. the$username and $password values submitted by the user) to its
constructor. We then simply call the authenticate() method. If successful, we pass the
identity information into the CWebUser::login method, which will store the identity
information into persistent storage (PHP session by default) for retrieval upon subsequent
requests. If the authentication fails, we can interrogate the errorMessage property for more
information as to why it failed.
Whether or not a user has been authenticated can easily be checked throughout the
application by using Yii::app()->user->isGuest. If using persistent storage like session (the
default) and/or a cookie (discussed below) to store the identity information, the user can
remain logged in upon subsequent requests. In this case, we don't need to use the
UserIdentity class and the entire login process upon each request. Rather CWebUser will
automatically take care of loading the identity information from this persistent storage and
will use it to determine whether Yii::app()->user->isGuest returns true or false.
Cookie-based Login
By default, a user will be logged out after a certain period of inactivity, depending on the
session configuration. To change this behavior, we can set the allowAutoLogin property of
the user component to be true and pass a duration parameter to the CWebUser::login
method. The user will then remain logged in for the specified duration, even if he closes
his browser window. Note that this feature requires the user's browser to accept cookies.
// Keep the user logged in for 7 days.
// Make sure allowAutoLogin is set true for the user component.
Yii::app()->user->login($identity,3600*24*7);
As we mentioned above, when cookie-based login is enabled, the states stored via
CBaseUserIdentity::setState will be saved in the cookie as well. The next time when the
user is logged in, these states will be read from the cookie and made accessible via
Yii::app()->user.