function get($assoc_type)
 {
     assert('$assoc_type == "HMAC-SHA1"');
     // $handle = sprintf( '{%s}%d/%d',  $assoc_type, localtime(), $this->count );
     $path = tempnam($this->store_dir, $assoc_type . '_');
     $handle = basename($path);
     $this->count += 1;
     $secret = oidUtil::random_string(20, null);
     $assoc = Association::from_expires_in($handle, $secret, $this->lifespan);
     $fh = fopen($path, 'w');
     if ($fh) {
         fwrite($fh, base64_encode(@serialize($assoc)));
         fclose($fh);
     }
     return $assoc;
 }