CakePHPのAuthComponent

cake/libs/controller/components/auth.php

    function user($key = null) {
        $this->__setDefaults();
        if (!$this->Session->check($this->sessionKey)) {
            return null;
        }

        if ($key == null) {
            $model =& $this->getModel();
            return array($model->alias => $this->Session->read($this->sessionKey));
        } else {
            $user = $this->Session->read($this->sessionKey);
            if (isset($user[$key])) {
                return $user[$key];
            }
            return null;
        }
    }

    function login($data = null) {
        $this->__setDefaults();
        $this->_loggedIn = false;

        if (empty($data)) {
            $data = $this->data;
        }

        if ($user = $this->identify($data)) {
            $this->Session->write($this->sessionKey, $user);
            $this->_loggedIn = true;
        }
        return $this->_loggedIn;
    }