Arduino for STM32

I'm currently using the official STM32 core and I want to know how I can make my chip, the STM32F303 Black Pill act as an SPI slave?

Did you try the SPI example,?

Which example? Both of the examples on Github under the SPI section seems to have the STM32 as an SPI master, not slave. My goal is that I want to have two STM32 devices communicate with each other using SPI.