Hi folks,
I've just committed significant changes Zest which allow it to perform client side actions.
For the Java reference implementation I've used Selenium, but other implementations can use any technology that maps to WebDriver.
So you can do things like launch browser windows, fill in forms and submit them.
I've also added code to support this in the ZAP add-on, so you can create and run Zest scripts that include client side actions graphically.
Note that you can mix and match server and client side statements - I have implemented a script (not yet released) which allows me to login to Persona (a SSO solution from Mozilla) using a browser and then reuse the session tokens for direct (non browser based) calls.
In ZAP you can use client side statements in any script apart from passive ones.
I'm not planning on releasing the ZAP Zest add-on right now, because I want to do some more testing, include some useful example scripts and write some documentation (theres none now;)
But if you do want to play with it then you can build it yourself or wait for the next weekly release.
Cheers,
Simon