Credentials Handling

[bdlukaa]

The problem

If the server credentials have changed, it is not possible to perform calls to it using the stored credentials.
Currently, the app is just not working, and the user may have no idea why.

Expected solution

Show an error message, banner, or badge saying that the server has issues and is using cached data. checkedServerCredentails returns {"success":false,"message":"Wrong login\/password combination, please try again."} when the credentials are incorrect.

Additionally, an option could be added to the settings asking the user to refresh the server credentials every X days for security reasons.