The title pretty much says it all on this one. I just started playing around with Ember, and one of the first things I tried to do was include the ember-simple-auth addon in a brand new project. I tried following the step-by-step instructions in the readme as well as the ones shown in the introductory video. Nothing I did seemed to work; I just kept getting the error Attempting to inject an unknown injection: 'service:session'.
It turns out, all that was required to resolve the error was to quit and restart the running ember server command. Apparently the live reload server doesn’t include newly installed addons―thanks to a GitHub comment for the hint!