Additional failure sources for background task

[teolemon]

The approach with if (storedUser.userId == currentUser.userId) … change password seems OK.
But it won't totally fix the issue, with this kind of flow:

User A : New background task
User A : new password + new login in the app
User B : login in the app

In that particular case, the background task won't use the latest password from User A.
Instead, I would "simply do": when a user logs in, iterate in all pending tasks and update the password if this is the relevant user.

Such behavior would allow notifying the user when we have some incorrect password error and quickly fix all issues

Originally posted by @g123k in #4869 (comment)