@Override
    public ByteSource getCredentialsSalt() {
        return credentialsSalt;
    }
Returns the salt used to hash the credentials, or {@code null} if no salt was used or credentials were not
hashed at all.
<p/>
Note that this attribute is <em>NOT</em> handled in the
{@link #merge(AuthenticationInfo) merge} method - a hash salt is only useful within a single realm (as each
realm will perform it's own Credentials Matching logic), and once finished in that realm, Shiro has no further
use for salts.  Therefore it doesn't make sense to 'merge' salts in a multi-realm scenario.

@return the salt used to hash the credentials, or {@code null} if no salt was used or credentials were not
hashed at all.
@since 1.1
core/src/main/java/org/apache/shiro/authc/SimpleAuthenticationInfo.java