This might be premature, but I think what you're doing here is brilliant. I know so many designers-come-web-developers who struggle with the back-end portion of web development. Many use cases simply don't need the full flexibility of a web app framework, but do need more than what you can cobble together with outside tools like the various embeddable form tools and widgets.

IMO, the authentication & authorization portion of your app is going to make or break the result. I'd like to make a suggestion. There is an authorization library for Rails named CanCan. It uses a declarative definition for authorization that is similar (loosely) to what you've got going right now. There is also an extension for CanCan called Cantango, which builds out the concept of roles as packages of permissions.

Again, I'm speaking really loosely here, but it looks like you're still working on this portion of the product, and these libraries work in a way that I think makes sense to your target market. The declarative style is a good fit for font end developers. You simply describe how you'd like users to interact with the API, and you're done. If you incorporated some of the ideas from these two libraries, I'd be really thrilled :)

Can't wait to recommend this.

https://github.com/ryanb/cancan

https://github.com/kristianmandrup/cantango