/**
* @phutil-external-symbol class PhabricatorStartup
*/
public function getCSRFToken()
{
$salt = PhabricatorStartup::getGlobal('csrf.salt');
if (!$salt) {
$salt = Filesystem::readRandomCharacters(self::CSRF_SALT_LENGTH);
PhabricatorStartup::setGlobal('csrf.salt', $salt);
}
// Generate a token hash to mitigate BREACH attacks against SSL. See
// discussion in T3684.
$token = $this->getRawCSRFToken();
$hash = PhabricatorHash::digest($token, $salt);
return 'B@' . $salt . substr($hash, 0, self::CSRF_TOKEN_LENGTH);
}