Present meaningful message to user when backend is unreachable

[kmichalikk]

Closes #1785

This PR refactors tokenVerification function in AuthService:

• extracts functions for user changin and parsing error messages coming from server
• adds null coalescence operator when using keycloak object to match type definitions

[grzanka]

I've switched on frontend and backend, selected some example and ran a simulation.
Then I saw the results in Z_profile tab.

Then I decided to disable backend.

Then I clicked on YZ_profile and saw two things:

• console log error "GET https://yap-dev.c3.plgrid.pl:8443/results?job_id=20250324-150205-1fb46e57-45bc-4f4c-b718-3f60b9d66e43DIRECT&estimator_name=yz_profile&page_numbers=0-2 net::ERR_CONNECTION_REFUSED"
• "loading circle" on YZ_profile tab

In that case I was expecting a good error message that backend is unreachable and app cannot display results.

Do you think this case can be handled in this PR or deserves another issue ?

Only after some time I got this:

The text "Keycloak User Rejected" is meaningless to the user, he doesn't know what is a keycloak.
It would be better to provide an URL of the unreachable backend.

[kmichalikk]

Do you think this case can be handled in this PR or deserves another issue ?

I think this case should be fixed separately because it comes from different component and different logic. Ideally, there should be some kind of global "middleware" that catches when backend is disconnected and shows the dialog, logs the user out, etc. Without that, we will be patching every component that fetches something from backend separately, which is redundant and inconsistent.

[grzanka]

Do you think this case can be handled in this PR or deserves another issue ?

I think this case should be fixed separately because it comes from different component and different logic. Ideally, there should be some kind of global "middleware" that catches when backend is disconnected and shows the dialog, logs the user out, etc. Without that, we will be patching every component that fetches something from backend separately, which is redundant and inconsistent.

Good idea ! Can you submit such an new issue ?

[kmichalikk]

#1988