code: private static function createExternalCaFile($baseFolder)
      {
          $path = \tempnam($baseFolder, "dropbox-php-sdk-trusted-certs");
          if ($path === false) {
              throw new \Exception("Couldn't create temp file in folder ".Util::q($baseFolder).".");
          }
          \register_shutdown_function(function() use ($path) {
              \unlink($path);
          });
  
          // NOTE: Can't use the standard PHP copy().  That would clobber the locked-down
          // permissions set by tempnam().
          self::copyInto(__DIR__.self::$originalPath, $path);
  
          return $path;
      }
docs: @param string $baseFolder
  
  @return string