Where is the code for nitrokey to check the integrity of the pc?

GitHub - Nitrokey/coreboot-builder: Builder Repository for Coreboot with Tianocore Firmware I saw the code of coreboot build here.
However, there seems to be no code in coreboot to check the integrity of the boot process in conjunction with nitrokey.
Is there any documented material and code on how nitrokey verifies the integrity of the boot process?
Thank you.

The Firmware used on the NitroPC is different compared to the Nitropads.
On the NitroPC there is no TPM, thus there is no possibility to reliably check the firmware for integrity. Tianocore (the UEFI Bios) built together with Coreboot is indeed open-source, but in terms of security different to Heads in exactly this point.