As described during the keynote, they’re magnetically held in place. You would need one set per user.

As someone that wears glasses with VR, it’s awful. The light gasket presses against them, gets tangled. The band presses against them. I can see why they didn’t bother making it an option, since I often put my headset away because of the discomfort. This is why the quest pro has optional light blockers, and why I never use mine. Leaving enough room for comfortably wearing glasses would make things huge.