public void setSalt(ByteSource salt) {
        this.salt = salt;
    }
Sets the salt used to previously compute AN ALREADY GENERATED HASH.
<p/>
This is provided <em>ONLY</em> to reconstitute a Hash instance that has already been computed.  It should ONLY
ever be invoked when re-constructing a hash instance from an already-hashed value.

@param salt the salt used to previously create the hash/digest.
@since 1.2
crypto/hash/src/main/java/org/apache/shiro/crypto/hash/SimpleHash.java