While 4.0.0-rc0 helps significantly, as we no longer need to wrap all the new additions; there have been some breaking changes in the Firebase JS SDK in 4.0.

Namely onAuthStateChanged is only fired on sign-in and sign-out, see the Firebase JS SDK changelog for more information.. onIdTokenChanged was added, which behaves as onAuthStateChanged used to.

So in addition to changing the dependency, we should add a new idToken observable which will wrap onIdTokenChanged.