Obtain an Access Token with an Authorization code

auth_code_gettoken.php

use GuzzleHttp\Client;
use GuzzleHttp\Exception\RequestException;
use League\OAuth2\Client\OptionProvider\HttpBasicAuthOptionProvider;
use League\OAuth2\Client\Provider\GenericProvider;
 
$setup_options = [
            'clientId'                => WSKEY,
            'clientSecret'            => SECRET,
            'redirectUri'             => 'http://localhost:8080/'
            'urlAuthorize'            => 'https://oauth.oclc.org/auth',
            'urlAccessToken'          => 'https://oauth.oclc.org/token',
            'urlResourceOwnerDetails' => '',
			'scopes'            => ['WorldCatMetadataAPI', 'refresh_token']            
        ];
                 
$basicAuth_provider = new HttpBasicAuthOptionProvider();
$provider = new GenericProvider($setup_options, ['optionProvider' => $basicAuth_provider]);

// If we don't have an authorization code then get one
if (!isset($_GET['code'])) {

    // Fetch the authorization URL from the provider; this returns the
    // urlAuthorize option and generates and applies any necessary parameters
    // (e.g. state).
    $authorizationUrl = $provider->getAuthorizationUrl();

    // Get the state generated for you and store it to the session.
    $_SESSION['oauth2state'] = $provider->getState();

    // Redirect the user to the authorization URL.
    header('Location: ' . $authorizationUrl);
    exit;

// Check given state against previously stored one to mitigate CSRF attack
} elseif (empty($_GET['state']) || (isset($_SESSION['oauth2state']) && $_GET['state'] !== $_SESSION['oauth2state'])) {

    if (isset($_SESSION['oauth2state'])) {
        unset($_SESSION['oauth2state']);
    }
    
    exit('Invalid state');

} else {

    try {

        // Try to get an access token using the authorization code grant.
        $accessToken = $provider->getAccessToken('authorization_code', [
            'code' => $_GET['code']
        ]);
        
        $url = SERVICE_URL . "/bib/data/1";   
	    $client = new Client();
	    $headers = array();
	    $headers['Authorization'] = "Bearer " . $accessToken->getToken();           
	    try {
	        $response = $client->request('GET', $url, ['headers' => $headers]);
	        $xml = $response->getBody();
	    } catch (RequestException $error) {
	        print_r($error);
	    }

    } catch (\League\OAuth2\Client\Provider\Exception\IdentityProviderException $e) {

        // Failed to get the access token or user details.
        exit($e->getMessage());

    }

}