code: private static function createExternalCaFolder($baseFolder)
      {
          // This is hacky, but I can't find a simple way to do this.
  
          // This process isn't atomic, so give it three tries.
          for ($i = 0; $i < 3; $i++) {
              $path = \tempnam($baseFolder, "dropbox-php-sdk-trusted-certs-empty-dir");
              if ($path === false) {
                  throw new \Exception("Couldn't create temp file in folder ".Util::q($baseFolder).".");
              }
              if (!\unlink($path)) {
                  throw new \Exception("Couldn't remove temp file to make way for temp dir: ".Util::q($path));
              }
              // TODO: Figure out how to make the folder private on Windows.  The '700' only works on Unix.
              if (!\mkdir($path, 700)) {
                  // Someone snuck in between the unlink() and the mkdir() and stole our path.
                  throw new \Exception("Couldn't create temp dir: ".Util::q($path));
              }
              \register_shutdown_function(function() use ($path) {
                  \rmdir($path);
              });
              return $path;
          }
  
          throw new \Exception("Unable to create temp dir in ".Util::q($baseFolder).", there's always something in the way.");
      }
docs: @param string $baseFolder
  
  @return string