This is similar to the ready signal, except it is called before
per-ref authentication. Apps can use this if they want to be able
to ask for user input on progress before asking for authentication.
This is nice to be able to do in general, but it is also required for
the implementation of
flatpak_installation_list_installed_refs_for_update(), as it doesn't
install any authentication handler, so it will never report updates
for protected refs if using the ready signal.
Note: In special cases we will require authentication even earlier
if authenticating is needed during the resolve operation. This happens
for instance if you are doing a update to a particular commit (rather
than the lastest commit) where we need to get the commit object directly.
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