Thanks for this thread this helped me a lot.
Device is a samsung S4 t-mobile variant.
The only trick is that on recovery, i'm using latest twrp, i needed to mount system in order to see the build.prop file.
notice. Device screen is totally broken, doesnt turn on. i was able to accomplish this without it.
after this then i proceeded with whats on the OP.
Update: it works but i get the Unauthorized device on adb shell, not i need to find out how to enable this since i can use the touch screen.
I was able to get an rsa key from another samsung s4 that was connected to the same computer, "adb_keys" is located in /data/misc/adb/
1. you must be rooted to take the adb_keys file from the phone that works. With es explorer "enabled root explorer" and i was able to see this file.
2. once you get a copy of adb_keys, reboot the phone with broken screen into recovery, adb recovery should work. im using twrp.
3.adb push <location of file>rsa_keys /data/misc/adb/
4. adb reboot and once the phone bots up voila! adb shell should be able to see the phone now.
i hope this helps someone like it did to me.