Redmine

I just wrote a script to collect projects via Rest-API and recognized that i cant filter projects with my URL.
If i click "show closed projects" in my browser it will redirect me to a page like:
/redmine/projects?closed=1

But using "closed" with json doesnt seem to work:
/redmine/projects.json?closed=1

Would be great if you could add more filters for projects, like "closed"

I hope this feature is not included yet and that i am not doing something wrong here ...
I am using version 2.1.2.stable