It would be great if you could share your insights into handling authentication with an API. I am still yet to find a perfect way to do it.
atm, we just use traditional rails authentication since our angular app is the only consumer of the api. But, that will be a bridge we need to cross soon and will post our findings. I would start by looking at how other market leaders do it, eg Stripe et al.
As far as connecting an angular app to backend api, I would look at this http://www.frederiknakstad.com/authentication-in-single-page...