[WIP] Allow re-authentication in editor after 401 response

This PR supersedes #3492.  The commit from #3492 has been rebased and is now working.  There are some UX and other minor details that need to be sorted out:

A couple things I noticed right away (there are likely others as well):
* There's currently no feedback after the re-authentication succeeds or fails.
* Credentials need to be cleared from the controller after the re-auth attempt.
* The modal needs to be styled.