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GitHub User: sohara
What do you mean? Thousands of sites/apps allow user sign up, but still require authentication to make sure a given user is who she claims to be. Authentication just means that you can add/change/delete resources, settings, etc. under your own account and not anyone else's. This screencast focussed only on the authentication side of things, but the developer is responsible for authorization, which is highly dependent on the kind of app being developed. Usually authentication is a bit more generic.