From [[http://www.yiichina.com/tutorial/332]]\\

Create a **''user''** table in the yii2basic database\\
<code mysql>
CREATE TABLE `user` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `username` varchar(50) NOT NULL,
  `password` varchar(32) NOT NULL,
  `authKey` varchar(100) NOT NULL DEFAULT '',
  `accessToken` varchar(100) NOT NULL DEFAULT '',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of myuser
-- ----------------------------
INSERT INTO `user` VALUES ('1', 'admin', '123', '1234', '1234');
INSERT INTO `user` VALUES ('2', 'demo', '234', '123', '123');
</code>

Make the following changes in **''models/User.php'**\\
<code php>
namespace app\models;

class User extends /*\yii\base\Object*/ \yii\db\ActiveRecord implements \yii\web\IdentityInterface
{
    /*public $id;
    public $username;
    public $password;
    public $authKey;
    public $accessToken;

    private static $users = [
        '100' => [
            'id' => '100',
            'username' => 'admin',
            'password' => 'admin',
            'authKey' => 'test100key',
            'accessToken' => '100-token',
        ],
        '101' => [
            'id' => '101',
            'username' => 'demo',
            'password' => 'demo',
            'authKey' => 'test101key',
            'accessToken' => '101-token',
        ],
    ];
*/

    /**
     * @inheritdoc
     */
    public static function tableName()
    {
        return 'user';
    }

    /**
     * @inheritdoc
     */
    public function rules()
    {
        return [
            [['username', 'password'], 'required'],
            [['username'], 'string', 'max' => 50],
            [['password'], 'string', 'max' => 32],
            [['authKey'], 'string', 'max' => 100],
            [['accessToken'], 'string', 'max' => 100],
        ];
    }

    /**
     * @inheritdoc
     */
    public function attributeLabels()
    {
        return [
            'id' => 'ID',
            'username' => 'Username',
            'password' => 'Password',
            'authKey' => 'AuthKey',
            'accessToken' => 'AccessToken',
        ];
    }

    /**
     * @inheritdoc
     */
    public static function findIdentity($id)
    {
        return static::findOne($id);
        //return isset(self::$users[$id]) ? new static(self::$users[$id]) : null;
    }

    /**
     * @inheritdoc
     */
    public static function findIdentityByAccessToken($token, $type = null)
    {
        return static::findOne(['access_token' => $token]);
        /*foreach (self::$users as $user) {
            if ($user['accessToken'] === $token) {
                return new static($user);
            }
        }

        return null;*/
    }

    /**
     * Finds user by username
     *
     * @param  string      $username
     * @return static|null
     */
    public static function findByUsername($username)
    {
          $user = User::find()
            ->where(['username' => $username])
            ->asArray()
            ->one();

            if($user){
            return new static($user);
        }

        return null;
        /*foreach (self::$users as $user) {
            if (strcasecmp($user['username'], $username) === 0) {
                return new static($user);
            }
        }

        return null;*/
    }

    /**
     * @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;
    }
}
</code>

That's all