Source code for Heltec nRF52 bootloader

Hi

I noticed that there is no source code available here for the bootloader. I guess it is based on the Arduino nRF52 Bootloader v0.9.0.

Are there any changes to the Arduino bootloader? Are you able to share the source code, or even just the board definition that was used? (board.h, board.mk and pinconfig.c)

Thanks