v-wordpress-plugin-updater/update-api/autoload.php

<?php

/**
 * Simple PSR-4 autoloader for the App namespace.
 */

spl_autoload_register(function ($class) {
    $prefix = 'App\\';
    $baseDir = __DIR__ . '/app/';
    $len = strlen($prefix);
    if (strncmp($prefix, $class, $len) !== 0) {
        return;
    }
    $relativeClass = substr($class, $len);
    $file = $baseDir . str_replace('\\', '/', $relativeClass) . '.php';
    if (file_exists($file)) {
        require_once $file;
    }
});