I think the part concat with salt is required. But generating it FOR the user is orthogonal to the hashing function. But I will be surprise if the paper actuall

I think the part concat with salt is required. But generating it FOR the user is orthogonal to the hashing function. But I will be surprise if the paper actually says it is required to generate one - because that shows the cleverness of the inventors, but also a potential weakness (implementation may be using weak random source, though counter-argument is that user supplied salt can be weak too).