Yii pass-through authorization by username?

Question

Yii

using getenv("username")
I can find out the current user. how to implement a button on the login tab to find out if there is such a user in the database? something like

else if (getenv("username") == $user->id )
        {
            $this->_id = $user->id;        
            $this->username = $user->login;
            $this->errorCode = self::ERROR_NONE;
        }

I can actually check it out.
login.php

<h1>Вход</h1>

<p></p>

<div class="form">
    <?php
    $form = $this->beginWidget('CActiveForm', array(
        'id' => 'login-form',
        'enableClientValidation' => true,
        'clientOptions' => array(
            'validateOnSubmit' => true,
        ),
    ));
    ?>

    <p class="note">Поля с <span class="required">*</span> обязательны.</p>

    <div class="row">		
        <?php echo CHtml::label('Имя', 'n'); ?>
        <?php echo $form->textField($model, 'username'); ?>
        <?php echo $form->error($model, 'username'); ?>
    </div>

    <div class="row">		
        <?php echo CHtml::label('Пароль', 'p'); ?>
        <?php echo $form->passwordField($model, 'password'); ?>
        <?php echo $form->error($model, 'password'); ?>
        <p class="hint">
            Для получения данных для входа обратитесь к администратору
        </p>
    </div>

    <div class="row rememberMe">
        <?php echo $form->checkBox($model, 'rememberMe'); ?>		
        <?php echo CHtml::label('Запомнить', 'r'); ?>  
        <?php echo $form->error($model, 'rememberMe'); ?>
    </div>

    <div class="row buttons">
        <?php echo CHtml::submitButton('Вход'); ?>

    </div>

    <?php $this->endWidget(); ?>
    <?php
    $form = $this->beginWidget('CActiveForm', array(
        'id' => 'ldap_login',
        'enableClientValidation' => true,
        'clientOptions' => array(
            'validateOnSubmit' => true,
        ),
    ));
    ?>
    <?php echo CHtml::submitButton('Вход под текущим пользователем'); ?>
    <?php $this->endWidget(); ?>
</div><!-- form -->

it is necessary that the second button in useridentity be checked

$ldapuser = User::model()->find('LOWER(login)=?', array(strtolower(getenv("username"))));

else if ($ldapuser)
        {
            $this->_id = $ldapuser->id;        
            $this->username = $ldapuser->login;
            $this->errorCode = self::ERROR_NONE;
        }