/**
* Register an get/post call. Important to prevent CSRF attacks.
*
* @return string The encrypted CSRF token, the shared secret is appended after the `:`.
*
* @description
* Creates a 'request token' (random) and stores it inside the session.
* Ever subsequent (ajax) request must use such a valid token to succeed,
* otherwise the request will be denied as a protection against CSRF.
* @see OC_Util::isCallRegistered()
*/
public static function callRegister()
{
// Use existing token if function has already been called
if (isset(self::$obfuscatedToken)) {
return self::$obfuscatedToken;
}
$tokenLength = 30;
// Check if a token exists
if (!\OC::$server->getSession()->exists('requesttoken')) {
// No valid token found, generate a new one.
$requestToken = \OC::$server->getSecureRandom()->getMediumStrengthGenerator()->generate($tokenLength);
\OC::$server->getSession()->set('requesttoken', $requestToken);
} else {
// Valid token already exists, send it
$requestToken = \OC::$server->getSession()->get('requesttoken');
}
// XOR the token to mitigate breach-like attacks
$sharedSecret = \OC::$server->getSecureRandom()->getMediumStrengthGenerator()->generate($tokenLength);
self::$obfuscatedToken = base64_encode($requestToken ^ $sharedSecret) . ':' . $sharedSecret;
return self::$obfuscatedToken;
}