Contao\FrontendUser::authenticate PHP Method

    public function authenticate()
    {
        // Default authentication
        if (parent::authenticate()) {
            return true;
        }
        // Check whether auto login is enabled
        if (\Config::get('autologin') > 0 && ($strCookie = \Input::cookie('FE_AUTO_LOGIN')) != '') {
            // Try to find the user by his auto login cookie
            if ($this->findBy('autologin', $strCookie) !== false) {
                // Check the auto login period
                if ($this->createdOn >= time() - \Config::get('autologin')) {
                    // Validate the account status
                    if ($this->checkAccountStatus() !== false) {
                        $this->setUserFromDb();
                        // Last login date
                        $this->lastLogin = $this->currentLogin;
                        $this->currentLogin = time();
                        $this->save();
                        // Generate the session
                        $this->generateSession();
                        $this->log('User "' . $this->username . '" was logged in automatically', __METHOD__, TL_ACCESS);
                        // Reload the page
                        \Controller::reload();
                        return true;
                    }
                }
            }
            // Remove the cookie if it is invalid to enable loading cached pages
            $this->setCookie('FE_AUTO_LOGIN', $strCookie, time() - 86400, null, null, \Environment::get('ssl'), true);
        }
        return false;
    }