While not really an authentication module itself (but more a core function of all modules), vouchers as a way for a user to authenticate come in 2 forms.
Printable Vouchers
Purchased Vouchers
Printable Vouchers
You can create these based off any Plan you have created in the system. These can be sold or simply given away to guests. You can create printable vouchers here.
Purchased Vouchers
These are created by the guest when they purchase online with Credit Card via the Stripe integration, or charge to their reservation if your site is set up for this with a PMS Integration that supports it.