Yii2 object oriented model API throwing error on execution

Question

I am creating an api using Yii2 framework . But it throws error during its execution.

BankDetailsController.php

<?php 

namespace backend\controllers;
use yii\rest\ActiveController;
use common\components\CustomAuth;


class BankDetailsController extends ActiveController
{
    public $modelClass = 'common\models\BankDetails';

    public function behaviors()
    {
        $behaviors = parent::behaviors();
        $behaviors['authenticator'] = [
            'class' => CustomAuth::className(),            
        ];
        return $behaviors;
    }
}

Admin.php

public function getUserIdFromToken($token){
        $sql = "select AdminUserID from utpl_opt_usertoken where auth_token =".$token;
        $userIdFromToken = Yii::$app->db->createCommand($sql)->queryAll();
        return $userIdFromToken;
    }

BankDetails.php

<?php

namespace common\models;
use yii\db\ActiveRecord;
use Yii;

class BankDetails extends ActiveRecord
{
    public static function tableName()
    {
        return 'th_bank_details';
    }

    public function fields()
    {
        return [ 'bank_name', 'branch_name' , 'ifsc_code' , 'account_type' , 'account_number' , 'name_on_account' , 'relationship' , 'user_id' , 'is_active' , 'listing_mode' , 'listing_user' , 'created_by' ];
    }

    public function rules()
    {
        return [
            [
                ['bank_name' , 'branch_name', 'account_type' , 'user_id' , 'is_active' , 'listing_mode' , 'listing_user', 'created_by' ],  'safe'
            ],
            [
                [ 'ifsc_code' , 'account_number' , 'name_on_account' , 'relationship'  ],  'required'
            ],
        ];
    }

    public function save($runValidation = true, $attributeNames = null)
    {   
        $id = Yii::$app->user->getId();
        $this->created_by = $id;
        return $this->insert($runValidation, $attributeNames);
    }
}

customAuth.php

<?php 

namespace common\components;
use yii\filters\auth\AuthMethod;
use common\models\Admin;

class CustomAuth extends AuthMethod
{
    public function authenticate($user, $request, $response)
    {
        //var_dump($request->getHeaders());
        $token = $request->getHeaders();
        $userId = Admin::getUserIdFromToken($token);
        $identity = Admin::findIdentity($userId);
        $user->login($identity);
        return $identity;
        return true;
    }
}

On execution this throws error as

{
  "name": "PHP Recoverable Error",
  "message": "Object of class yii\\web\\HeaderCollection could not be converted to string",
  "code": 4096,
  "type": "yii\\base\\ErrorException",
  "file": "C:\\xampp\\htdocs\\app\\common\\models\\Admin.php",
  "line": 98,
}

Any help would be great.... Thank you