session_start();
 
$provider = new \Calcinai\OAuth2\Client\Provider\Xero([
    'clientId'          => '{xero-client-id}',
    'clientSecret'      => '{xero-client-secret}',
    'redirectUri'       => 'https://example.com/callback-url',
]);
 
if (!isset($_GET['code'])) {

    // If we don't have an authorization code then get one
    $authUrl = $provider->getAuthorizationUrl([
        'scope' => 'openid email profile accounting.transactions'
    ]);

    $_SESSION['oauth2state'] = $provider->getState();
    header('Location: ' . $authUrl);
    exit;

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

    unset($_SESSION['oauth2state']);
    exit('Invalid state');

} else {

    // Try to get an access token (using the authorization code grant)
    $token = $provider->getAccessToken('authorization_code', [
        'code' => $_GET['code']
    ]);


    //If you added the openid/profile scopes you can access the authorizing user's identity.
    $identity = $provider->getResourceOwner($token);
    print_r($identity);

    //Get the tenants that this user is authorized to access
    $tenants = $provider->getTenants($token);
    print_r($tenants);
}

$provider = new \Calcinai\OAuth2\Client\Provider\Xero([
   'clientId'          => '{xero-client-id}',
   'clientSecret'      => '{xero-client-secret}',
   'redirectUri'       => 'https://example.com/callback-url',
]);
   
$authUrl = $provider->$provider->getAuthorizationUrl([
   'scope' => 'bankfeeds accounting.transactions'
]);

$newAccessToken = $provider->getAccessToken('refresh_token', [
    'refresh_token' => $existingAccessToken->getRefreshToken()
]);