Any of the possible button actions can also be assigned to a virtual RFID card. Those cards then can be assigned on the web GUI like normal cards but use special 12-digit IDs: 900000000001 - 900000000009.
To assign a virtual RFID card, just press the configured button action, the virtual RFID automatically gets filled in in the web GUI:
Note: Make sure you have configured the button action beforehand in settings.h, eg:
#define BUTTON_2_LONG CMD_VIRTUAL_RFID_CARD_01