A variac+rectifier would work okay, but IanP said, it will be unregulated. A good solution would be to use a simple discrete current regulator on the DC output. A current regulator is probably a good idea even if you go with a regulated voltage source.
I'd advise against fancy PWM controllers like the FSFR2100, unless you already are familiar with LLC resonant converters and are capable of making the necessary transformer (most people can't do that).
If you have the parts on hand for doing the variac+rectifier+regulator, I would give that a shot. If you don't, and have to spend some money in either case, I would just buy the supplies.