[cz.mafra.jizdnirady] app google login not working when using MicroG

[litoj]

Affected app
Name: IDOS
Package id: cz.mafra.jizdnirady

Describe the bug

The app has a google login method that shows me the microg account selector correctly populated with the one account I have logged in. But selecting it just closes the dialog and the requesting app prints an error translatable as "Connecting via external service failed."

To Reproduce
Steps to reproduce the behavior:

1. Go to the tab with burger icon (last right tab)
2. Click on user profile icon (first in the tab)
3. Click on "Google" to select a google account
4. After you select an account, the app shows an error (popup dialog)

Expected behavior
I get logged in.

Screenshots

System
Android Version: 11
Custom ROM: CorvusOS 16.8

microG
microG Core version: v0.3.6.244735
microG Self-Check results: after installing the latest the signature spoofing no longer works so that makes 3 checkboxes unticked, but they were before on 3.2.xxx and the behaviour was the same.

[ale5000-git]

The problem is NOT what it seems, microG correctly detect that your ROM doesn't have the "updated" signature spoofing patch.
The API used to check signature may return the result in 2 different ways; previously only the first way was used by apps and so previous signature spoofing patches patch only the first way.

Now the Google libraries used by various apps (so inside the various apps) got updated to use the second way of the API (the API is inside the system, so it can't be changed without a full system update).

You can see the details here: #2680
And you can see the minimum version of the ROM that you need here: #2680 (comment)

If you cannot update or recompile your ROM the only solution is to use FakeGApps.