So far, using RSA-PSS, it is caller's responsibility to prepare the input data like:
```
(data (flag pss)
(hash <algo> <hashed-value>)
(random-override <salt>))
```
with `<HASHED-VALUE>` (it is the caller who does hashing, beforehand).
It is good to have "prehash" function (in RFC 8032 (EdDSA) terminology) which hashes input internally when pk_sign-ed. The data format to use this functionality will be:
```
(data (flags pss
prehash)
(hash-algo <algo>)
(value <value>))
```