You have discovered a cross-site request forgery vulnerability in the application that a client has published on the web. Which recommendation can you make to mitigate this vulnerability?
1) The client should switch from using GET to POST as CSRF can not be exploited via POST.
2) The client should add a value to the processing script that cannot be predicted by an attacker.
3) The client should issue stronger, random session IDs to application users.
4) The client should treat all inputs as malicious and validate them.