Comment 5 for bug 745638

In a practical sense USC can already know that the user has authenticated but in every instances, the spawnedf helper app looks for the token and gives it to the server, so there is technically a 'sign in' step even though it is a formality if you've already signed in (unless the server has revoked the token in the interim).
Note when I talk about signing in, in this sense, I'm not talking about the user entering any credentials (or even any dialog showing) but more the process that is happening in the background between the client and server to 'handshake' before allowing submission.