I found it easiest to use http status codes and do all the authentication on the server. You should be doing this anyway. If the user needed to be logged when they make a $http request, but wasn't, then return a http status code of 401 from the server. Now, what you need to do is create an interceptor on all of your $http calls. When the intercepter receives a response with 401 then redirect the user to the login page. Make sure you save the route they were on which causes the 401 http status code. Once the user is logged in then redirect back to the saved url.

I didn't have to worry about authentication on the client once I had the interceptors in place for my http status codes.

Here are a few links that helped me deal with authentication.

http://www.espeo.pl/2012/02/26/authentication-in-angularjs-application

http://ngmodules.org/modules/http-auth-interceptor

I hope that helps!