Either by allowing multiple sign-ins, or some other way.
For details, see here:
"Constraint: this approach requires all simultaneously accessed back-ends to to use the same protocol and (by extension) the same code. Ideally, we would like to make it possible for any community to run their own for of Hypothes.is (backend, frontend, whatever.)"
I believe this statement is false or overblown. The login is currently done inline, in the sidebar. I dislike this because it:
If that issue is removed (e.g., by implementing our sign-in by creating a BrowserID identity provider for @hypothes.is), then we would have a demonstrated ability to support arbitrary custom login flows and the client would only need to get the token back from the flow. The annotator-store API would have to change to accept these tokens instead of the current system. However, beyond that, the store API is something that we should promote, stabilize, and standardize, and I think it's acceptable that all backends would understand it.