In Manitoba, Canada, we have proof-of-vaccination cards and an app for verifying them.
The app is not open source and I wanted to look at it, so this is the Android APK unpacked using apktool.
The app appears to be written in Expo framework and therefore the meat of the app is a single Javascript bundle, which I have unminified here. This bundle is pretty big (almost 5MB) so I pulled out some of the interesting (to me) snippets, particularly around how the QR code is handled, in a Gist, here.
There really are no goals with this, I just wanted to do some of the legwork for others in case they wanted to look more closely at the app.