Multiple database connections and Yii 2.0

You can implement database user management using extesions like https://github.com/amnah/yii2-user.

OR

If you want to write your own custom script to manage the users you can override Yii2 identityClass.

In the component section of your config add:

'user' => [
        'identityClass'   => 'app\models\User',
        'enableAutoLogin' => true,
    ],

Please note that your user model MUST IMPLEMENT \yii\web\IdentityInterface

Here is the example of the model class that you can use to implement database authentication

namespace app\models;

//app\models\gii\Users is the model generated using Gii from users table

use app\models\gii\Users as DbUser;

class User extends \yii\base\Object implements \yii\web\IdentityInterface {

public $id;
public $username;
public $password;
public $authKey;
public $accessToken;
public $email;
public $phone_number;
public $user_type;

/**
 * @inheritdoc
 */
public static function findIdentity($id) {
    $dbUser = DbUser::find()
            ->where([
                "id" => $id
            ])
            ->one();
    if (!count($dbUser)) {
        return null;
    }
    return new static($dbUser);
}

/**
 * @inheritdoc
 */
public static function findIdentityByAccessToken($token, $userType = null) {

    $dbUser = DbUser::find()
            ->where(["accessToken" => $token])
            ->one();
    if (!count($dbUser)) {
        return null;
    }
    return new static($dbUser);
}

/**
 * Finds user by username
 *
 * @param  string      $username
 * @return static|null
 */
public static function findByUsername($username) {
    $dbUser = DbUser::find()
            ->where([
                "username" => $username
            ])
            ->one();
    if (!count($dbUser)) {
        return null;
    }
    return new static($dbUser);
}

/**
 * @inheritdoc
 */
public function getId() {
    return $this->id;
}

/**
 * @inheritdoc
 */
public function getAuthKey() {
    return $this->authKey;
}

/**
 * @inheritdoc
 */
public function validateAuthKey($authKey) {
    return $this->authKey === $authKey;
}

/**
 * Validates password
 *
 * @param  string  $password password to validate
 * @return boolean if password provided is valid for current user
 */
public function validatePassword($password) {
    return $this->password === $password;
}

}

I hope that would be helpful to you . Cheers :)

If you use ActiveForm widget use this:

<?php 
    $items = ArrayHelper::map(Model::find()->all(), 'id', 'name');
    $form->field($model, 'attribute')->dropDownList($items)
?>