Is there a way to allow access to specific folder in Google Drive with Googl Picker on the backend?

Question

My application intends to read all files in users selected folder. Users should be able to select folder using Google Picker.

I have read the documentation for the scope. I think drive.file should be enough for my use case. The only problem is I still don't understand how can I setup the code on backend to use specific files chosen by the frontend.