How to config ENV_IS_IN_NAND to default option in Kconfig?

Hi all:

I'm intend to set ENV_IS_IN_NAND to my default option in env/Kconfig. I can see the ENV_IS_IN_NAND is depends on !CHAIN_OF_TRUST, but I don't know where CHAIN_OF_TRUST is configured from. So where should I define this CHAIN_OF_TRUST in Kconfig? And What does CHAIN_OF_TRUST do?

Thanks Amada.Minami