This happened to me in Mumbai several years ago. I had thankfully been forewarned, but there were military police checking boarding passes for entering passengers outside the airport, and no one without a paper boarding pass + appropriate government ID was allowed into the terminal. This was right up there with the "requirement" that business travelers in India provide a physical business card to the hotel when checking in. I haven't been a in few years, so hopefully that's at least no longer the case.