salt(
length) ->salt
Generate a random binary salt string
Returns a string of length random bytes (default 16) from the kernel
CSPRNG. The output is raw binary, NOT hex-encoded. Byte value 0x00 is
excluded. Suitable for use as HMAC key material or a password-hashing
salt.
Returns nil, err if the kernel entropy source cannot be read. Callers
must not paper over that: a salt that silently degrades is the failure
this function exists to prevent.