Access sha256 as a txn converter within Lua script

Hey there,

I’d like to use sha256 hashing algo apparently provided as an haproxy converter within my Lua script.

sha1 works : txn.c:sha1(str)

but sha2 does not seem to work, or perhaps I am using it wrong : txn.c:sha2(256)

It would be really helpful if someone could comment here with an example of sha256 converter usage.