I’m playing with Sencha Touch right now in a Rails app. One of the things that hung me up for a bit was the authenticity token that is required with POSTing form data to the rails controller. Here is how I did it.
In the Sencha file where you declare your FormPanel capture the Rails csrf_token as a variable by adding the following:
var csrf_token = document.getElementsByName("csrf-token").getAttribute("content");
In your FormPanel create a hidden field to submit the token to the controller
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Now when you submit the form your authenticity token will be submitted and you can keep the cross-site-scripting forgery protection that Rails provides