OAuth-based authentication getting issue

hi i am trying to create OAuth-based authentication by following official doc https://devdocs.magento.com/guides/v2.3/get-started/authentication/gs-authentication-oauth.html

but when i click on login i am getting this below issue

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
require './vendor/autoload.php';

$consumerKey = $_REQUEST['oauth_consumer_key'];
$callback = $_REQUEST['callback_url'];

session_id('test');
session_start();

/** Use $consumerKey to retrieve the following data in case it was stored in DB when received at "endpoint.php" */
if ($consumerKey !== $_SESSION['oauth_consumer_key']) {
    throw new \Exception("Consumer keys received on different requests do not match.");
}

$consumerSecret = $_SESSION['oauth_consumer_secret'];
$magentoBaseUrl = rtrim($_SESSION['store_base_url'], '/');
$oauthVerifier = $_SESSION['oauth_verifier'];

define('TESTS_BASE_URL', $magentoBaseUrl);

$credentials = new \OAuth\Common\Consumer\Credentials($consumerKey, $consumerSecret, $magentoBaseUrl);
$oAuthClient = new OauthClient($credentials);
$requestToken = $oAuthClient->requestRequestToken();
$accessToken = $oAuthClient->requestAccessToken(
    $requestToken->getRequestToken(),
    $oauthVerifier,
    $requestToken->getRequestTokenSecret()
);

header("location: $callback");

and this is the error avaialbe in reporting

Warning: require(./vendor/autoload.php): failed to open stream: No such file or directory in /var/www/html/localdev/pramod/pub/checklogin.php on line 4

Fatal error: require(): Failed opening required './vendor/autoload.php' (include_path='.:/usr/share/php') in /var/www/html/localdev/pramod/pub/checklogin.php on line 4

or does anyone have any other documentation or can guide me on this issue