How to use the TrustZone functions?

So, is it possible to use the crypto functions that are part of the ARM TrustZone CryptoCell? How?

While in theory you could call it from user firmware using the nRF5 SDK or directly using registers, it’s currently used by the system for AES, ECP, SHA1, and SHA256, and I believe you could run into issues with two different things trying to access the hardware at the same time.

So my app would like to use it for those same reasons, too. If I can’t use the TrustZone directly, could the base system export functions to do so safely?