common\models\User::generatePasswordResetToken PHP Method

    public function generatePasswordResetToken()
    {
        $this->password_reset_token = Yii::$app->security->generateRandomString() . '_' . time();
    }

 public function generateToken()
 {
     $mobile = $this->_session['passwordResetMobile'];
     $this->_user = User::findByMobile($mobile);
     if (!User::isPasswordResetTokenValid($this->_user->password_reset_token)) {
         $this->_user->generatePasswordResetToken();
     }
     return $this->_user->save(false);
 }