I'm doing the same thing when I go to the cinema or when I take the train: I show or give my phone to allow the entitled person to check a PDF or a barcode that proves I am allowed to be here.
When I do that my phone is unlocked.
Police, robbers can steal my unlocked phone when I do that.
Stupid joke but if Julian Assange needs to show a barcode when he goes to the cinema, he needs to present his unlocked phone to a stranger.
I'm not Assange, but today I felt very stupid when a city policeman (not a state policeman) asked me for my document when I was in the street with my wife and kids. I didn't trust him because he was obviously a city security guard and not a policeman, I asked if he had the authorization to perform this check, but in the end I gave him my unlocked phone to allow him to check my document (everything was OK according to the law).
Conclusion: I need an app to share only some selected files from the screen lock.
When I take the train, I need to "share" for some hours my traveling documents to this app, it will allow me to pass the barcode scanners without unlocking my phone.
I think the HN people might consider this coding opportunity.
