Using StringDigester for attribute hash function for consent ?

[Tom Zeller]

I'm thinking I should use Brent's StringDigester, and I'm wondering
about the salt. Basically, do I need to set the salt, and if so, what
do I set it to ?

Background : for consent, we calculate and store a hash of an IdP
attribute's values so we can determine if the attribute's values have
changed and hence prompt the user to consent again.

Currently I'm using Cryptacular's CodecUtil and HashUtil, but I don't
think a salt is available - I'm probably wrong though.

I kind of know the answer to my question, but advice is appreciated.

Thanks.