Yep the ST-Link Utility coupled with the Spark JTAG programmer shield is what you need.
Just load that bootloader bin and program it to the default address of 0x8000000 and the proverbial Bob is your uncle. You can also use the utility to program the core-firmware to address 0x8005000 easily. DFU over USB works super fast too once you have the bootloader installed.
I’m sure there are other open source solutions out there that could be made to work on a Mac, but I don’t know what they are.
Full guide here: